[RFC PATCH 0/2] mm: improve folio refcount scalability

[RFC PATCH 0/2] mm: improve folio refcount scalability

[Gladyshev Ilya]

Intro
=====
This patch optimizes small file read performance and overall folio refcount
scalability by refactoring page_ref_add_unless [core of folio_try_get].
This is alternative approach to previous attempts to fix small read
performance by avoiding refcount bumps [1][2].

Overview
========
Current refcount implementation is using zero counter as locked (dead/frozen)
state, which required CAS loop for increments to avoid temporary unlocks in
try_get functions. These CAS loops became a serialization point for otherwise
scalable and fast read side.

Proposed implementation separates "locked" logic from the counting, allowing
the use of optimistic fetch_add() instead of CAS. For more details, please
refer to the commit message of the patch itself.

Proposed logic maintains the same public API as before, including all existing
memory barrier guarantees.

Drawbacks
=========
In theory, an optimistic fetch_add can overflow the atomic_t and reset the
locked state. Currently, this is mitigated via a single CAS operation after
the "failed" fetch_add, which tries to reset the counter to a locked zero.
While this best-effort approach doesn't have any strong guarantees, it's
unrealistic that there will be 2^31 highly contended try_get calls on a locked
folio, and in each of these calls, the CAS operation will fail.

If this guarantee isn't sufficient, it can be improved by performing a full
CAS loop when the counter is approaching overflow.

Performance
===========
Performance was measured using a simple custom benchmark based on
will-it-scale[3]. This benchmark spawns N pinned threads/processes that
execute the following loop:
``
char buf[]
fd = open(/* same file in tmpfs */);

while (true) {
    pread(fd, buf, /* read size = */ 64, /* offset = */0)
}
``
While this is a synthetic load, it does highlight existing issue and
doesn't differ a lot from benchmarking in [2] patch.

This benchmark measures operations per second in the inner loop and the
results across all workers. Performance was tested on top of v6.15 kernel[4]
on two platforms. Since threads and processes showed similar performance on
both systems, only the thread results are provided below. The performance
improvement scales linearly between the CPU counts shown.

Platform 1: 2 x E5-2690 v3, 12C/12T each [disabled SMT]

#threads | vanilla | patched | boost (%)
       1 | 1343381 | 1344401 |  +0.1
       2 | 2186160 | 2455837 | +12.3
       5 | 5277092 | 6108030 | +15.7
      10 | 5858123 | 7506328 | +28.1
      12 | 6484445 | 8137706 | +25.5
         /* Cross socket NUMA */
      14 | 3145860 | 4247391 | +35.0
      16 | 2350840 | 4262707 | +81.3
      18 | 2378825 | 4121415 | +73.2
      20 | 2438475 | 4683548 | +92.1
      24 | 2325998 | 4529737 | +94.7

Platform 2: 2 x AMD EPYC 9654, 96C/192T each [enabled SMT]

#threads | vanilla | patched | boost (%)
       1 | 1077276 | 1081653 |  +0.4
       5 | 4286838 | 4682513 |  +9.2
      10 | 1698095 | 1902753 | +12.1
      20 | 1662266 | 1921603 | +15.6
      49 | 1486745 | 1828926 | +23.0
      97 | 1617365 | 2052635 | +26.9
         /* Cross socket NUMA */
     105 | 1368319 | 1798862 | +31.5
     136 | 1008071 | 1393055 | +38.2
     168 |  879332 | 1245210 | +41.6
               /* SMT */
     193 |  905432 | 1294833 | +43.0
     289 |  851988 | 1313110 | +54.1
     353 |  771288 | 1347165 | +74.7

[1] https://lore.kernel.org/linux-mm/CAHk-=wj00-nGmXEkxY=-=Z_qP6kiGUziSFvxHJ9N-cLWry5zpA@mail.gmail.com/
[2] https://lore.kernel.org/linux-mm/20251017141536.577466-1-kirill@shutemov.name/
[3] https://github.com/antonblanchard/will-it-scale
[4] There were no changes to page_ref.h between v6.15 and v6.18 or any
    significant performance changes on the read side in mm/filemap.c

Gladyshev Ilya (2):
  mm: make ref_unless functions unless_zero only
  mm: implement page refcount locking via dedicated bit

 include/linux/mm.h         |  2 +-
 include/linux/page-flags.h |  9 ++++++---
 include/linux/page_ref.h   | 35 ++++++++++++++++++++++++++---------
 3 files changed, 33 insertions(+), 13 deletions(-)

-- 
2.43.0

[RFC PATCH 1/2] mm: make ref_unless functions unless_zero only

[Gladyshev Ilya]

There are no users of (folio/page)_ref_add_unless(page, nr, u) with
u != 0 [1] and all current users are "internal" for page refcounting API.
This allows us to safely drop this parameter and reduce function
semantics to the "unless zero" cases only, which will be optimized in
the following patch.

If needed, these functions for the u!=0 cases can be trivially
reintroduced later using the same atomic_add_unless operations as before.

[1]: The last user was dropped in v5.18 kernel, commit 27674ef6c73f
("mm: remove the extra ZONE_DEVICE struct page refcount"). There is no
trace of discussion as to why this cleanup wasn't done earlier.

Co-developed-by: Gorbunov Ivan <gorbunov.ivan@h-partners.com>
Signed-off-by: Gorbunov Ivan <gorbunov.ivan@h-partners.com>
Signed-off-by: Gladyshev Ilya <gladyshev.ilya1@h-partners.com>
---
 include/linux/mm.h         |  2 +-
 include/linux/page-flags.h |  6 +++---
 include/linux/page_ref.h   | 14 +++++++-------
 3 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7c79b3369b82..f652426cc218 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1115,7 +1115,7 @@ static inline int folio_put_testzero(struct folio *folio)
  */
 static inline bool get_page_unless_zero(struct page *page)
 {
-	return page_ref_add_unless(page, 1, 0);
+	return page_ref_add_unless_zero(page, 1);
 }
 
 static inline struct folio *folio_get_nontail_page(struct page *page)
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 0091ad1986bf..7c2195baf4c1 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -231,7 +231,7 @@ static __always_inline const struct page *page_fixed_fake_head(const struct page
 	return page;
 }
 
-static __always_inline bool page_count_writable(const struct page *page, int u)
+static __always_inline bool page_count_writable(const struct page *page)
 {
 	if (!static_branch_unlikely(&hugetlb_optimize_vmemmap_key))
 		return true;
@@ -257,7 +257,7 @@ static __always_inline bool page_count_writable(const struct page *page, int u)
 	 * The refcount check also prevents modification attempts to other (r/o)
 	 * tail pages that are not fake heads.
 	 */
-	if (atomic_read_acquire(&page->_refcount) == u)
+	if (!atomic_read_acquire(&page->_refcount))
 		return false;
 
 	return page_fixed_fake_head(page) == page;
@@ -268,7 +268,7 @@ static inline const struct page *page_fixed_fake_head(const struct page *page)
 	return page;
 }
 
-static inline bool page_count_writable(const struct page *page, int u)
+static inline bool page_count_writable(const struct page *page)
 {
 	return true;
 }
diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h
index 544150d1d5fd..b0e3f4a4b4b8 100644
--- a/include/linux/page_ref.h
+++ b/include/linux/page_ref.h
@@ -228,14 +228,14 @@ static inline int folio_ref_dec_return(struct folio *folio)
 	return page_ref_dec_return(&folio->page);
 }
 
-static inline bool page_ref_add_unless(struct page *page, int nr, int u)
+static inline bool page_ref_add_unless_zero(struct page *page, int nr)
 {
 	bool ret = false;
 
 	rcu_read_lock();
 	/* avoid writing to the vmemmap area being remapped */
-	if (page_count_writable(page, u))
-		ret = atomic_add_unless(&page->_refcount, nr, u);
+	if (page_count_writable(page))
+		ret = atomic_add_unless(&page->_refcount, nr, 0);
 	rcu_read_unlock();
 
 	if (page_ref_tracepoint_active(page_ref_mod_unless))
@@ -243,9 +243,9 @@ static inline bool page_ref_add_unless(struct page *page, int nr, int u)
 	return ret;
 }
 
-static inline bool folio_ref_add_unless(struct folio *folio, int nr, int u)
+static inline bool folio_ref_add_unless_zero(struct folio *folio, int nr)
 {
-	return page_ref_add_unless(&folio->page, nr, u);
+	return page_ref_add_unless_zero(&folio->page, nr);
 }
 
 /**
@@ -261,12 +261,12 @@ static inline bool folio_ref_add_unless(struct folio *folio, int nr, int u)
  */
 static inline bool folio_try_get(struct folio *folio)
 {
-	return folio_ref_add_unless(folio, 1, 0);
+	return folio_ref_add_unless_zero(folio, 1);
 }
 
 static inline bool folio_ref_try_add(struct folio *folio, int count)
 {
-	return folio_ref_add_unless(folio, count, 0);
+	return folio_ref_add_unless_zero(folio, count);
 }
 
 static inline int page_ref_freeze(struct page *page, int count)
-- 
2.43.0

[RFC PATCH 2/2] mm: implement page refcount locking via dedicated bit

[Gladyshev Ilya]

The current atomic-based page refcount implementation treats zero
counter as dead and requires a compare-and-swap loop in folio_try_get()
to prevent incrementing a dead refcount. This CAS loop acts as a
serialization point and can become a significant bottleneck during
high-frequency file read operations.

This patch introduces FOLIO_LOCKED_BIT to distinguish between a
(temporary) zero refcount and a locked (dead/frozen) state. Because now
incrementing counter doesn't affect it's locked/unlocked state, it is
possible to use an optimistic atomic_fetch_add() in
page_ref_add_unless_zero() that operates independently of the locked bit.
The locked state is handled after the increment attempt, eliminating the
need for the CAS loop.

Co-developed-by: Gorbunov Ivan <gorbunov.ivan@h-partners.com>
Signed-off-by: Gorbunov Ivan <gorbunov.ivan@h-partners.com>
Signed-off-by: Gladyshev Ilya <gladyshev.ilya1@h-partners.com>
---
 include/linux/page-flags.h |  5 ++++-
 include/linux/page_ref.h   | 25 +++++++++++++++++++++----
 2 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 7c2195baf4c1..f2a9302104eb 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -196,6 +196,9 @@ enum pageflags {
 
 #define PAGEFLAGS_MASK		((1UL << NR_PAGEFLAGS) - 1)
 
+/* Most significant bit in page refcount */
+#define PAGEREF_LOCKED_BIT	(1 << 31)
+
 #ifndef __GENERATING_BOUNDS_H
 
 #ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
@@ -257,7 +260,7 @@ static __always_inline bool page_count_writable(const struct page *page)
 	 * The refcount check also prevents modification attempts to other (r/o)
 	 * tail pages that are not fake heads.
 	 */
-	if (!atomic_read_acquire(&page->_refcount))
+	if (atomic_read_acquire(&page->_refcount) & PAGEREF_LOCKED_BIT)
 		return false;
 
 	return page_fixed_fake_head(page) == page;
diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h
index b0e3f4a4b4b8..98717fd25306 100644
--- a/include/linux/page_ref.h
+++ b/include/linux/page_ref.h
@@ -64,7 +64,12 @@ static inline void __page_ref_unfreeze(struct page *page, int v)
 
 static inline int page_ref_count(const struct page *page)
 {
-	return atomic_read(&page->_refcount);
+	int val = atomic_read(&page->_refcount);
+
+	if (unlikely(val & PAGEREF_LOCKED_BIT))
+		return 0;
+
+	return val;
 }
 
 /**
@@ -176,6 +181,9 @@ static inline int page_ref_sub_and_test(struct page *page, int nr)
 {
 	int ret = atomic_sub_and_test(nr, &page->_refcount);
 
+	if (ret)
+		ret = !atomic_cmpxchg_relaxed(&page->_refcount, 0, PAGEREF_LOCKED_BIT);
+
 	if (page_ref_tracepoint_active(page_ref_mod_and_test))
 		__page_ref_mod_and_test(page, -nr, ret);
 	return ret;
@@ -204,6 +212,9 @@ static inline int page_ref_dec_and_test(struct page *page)
 {
 	int ret = atomic_dec_and_test(&page->_refcount);
 
+	if (ret)
+		ret = !atomic_cmpxchg_relaxed(&page->_refcount, 0, PAGEREF_LOCKED_BIT);
+
 	if (page_ref_tracepoint_active(page_ref_mod_and_test))
 		__page_ref_mod_and_test(page, -1, ret);
 	return ret;
@@ -231,11 +242,17 @@ static inline int folio_ref_dec_return(struct folio *folio)
 static inline bool page_ref_add_unless_zero(struct page *page, int nr)
 {
 	bool ret = false;
+	int val;
 
 	rcu_read_lock();
 	/* avoid writing to the vmemmap area being remapped */
-	if (page_count_writable(page))
-		ret = atomic_add_unless(&page->_refcount, nr, 0);
+	if (page_count_writable(page)) {
+		val = atomic_add_return(nr, &page->_refcount);
+		ret = !(val & PAGEREF_LOCKED_BIT);
+
+		if (unlikely(!ret))
+			atomic_cmpxchg_relaxed(&page->_refcount, val, PAGEREF_LOCKED_BIT);
+	}
 	rcu_read_unlock();
 
 	if (page_ref_tracepoint_active(page_ref_mod_unless))
@@ -271,7 +288,7 @@ static inline bool folio_ref_try_add(struct folio *folio, int count)
 
 static inline int page_ref_freeze(struct page *page, int count)
 {
-	int ret = likely(atomic_cmpxchg(&page->_refcount, count, 0) == count);
+	int ret = likely(atomic_cmpxchg(&page->_refcount, count, PAGEREF_LOCKED_BIT) == count);
 
 	if (page_ref_tracepoint_active(page_ref_freeze))
 		__page_ref_freeze(page, count, ret);
-- 
2.43.0

Re: [RFC PATCH 2/2] mm: implement page refcount locking via dedicated bit

[Kiryl Shutsemau]

On Fri, Dec 19, 2025 at 12:46:39PM +0000, Gladyshev Ilya wrote:
> The current atomic-based page refcount implementation treats zero
> counter as dead and requires a compare-and-swap loop in folio_try_get()
> to prevent incrementing a dead refcount. This CAS loop acts as a
> serialization point and can become a significant bottleneck during
> high-frequency file read operations.
> 
> This patch introduces FOLIO_LOCKED_BIT to distinguish between a

s/FOLIO_LOCKED_BIT/PAGEREF_LOCKED_BIT/

> (temporary) zero refcount and a locked (dead/frozen) state. Because now
> incrementing counter doesn't affect it's locked/unlocked state, it is
> possible to use an optimistic atomic_fetch_add() in
> page_ref_add_unless_zero() that operates independently of the locked bit.
> The locked state is handled after the increment attempt, eliminating the
> need for the CAS loop.

I don't think I follow.

Your trick with the PAGEREF_LOCKED_BIT helps with serialization against
page_ref_freeze(), but I don't think it does anything to serialize
against freeing the page under you.

Like, if the page in the process of freeing, page allocator sets its
refcount to zero and your version of page_ref_add_unless_zero()
successfully acquirees reference for the freed page.

How is it safe?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [RFC PATCH 2/2] mm: implement page refcount locking via dedicated bit

[Gladyshev Ilya]

On 12/19/2025 5:50 PM, Kiryl Shutsemau wrote:
> On Fri, Dec 19, 2025 at 12:46:39PM +0000, Gladyshev Ilya wrote:
>> The current atomic-based page refcount implementation treats zero
>> counter as dead and requires a compare-and-swap loop in folio_try_get()
>> to prevent incrementing a dead refcount. This CAS loop acts as a
>> serialization point and can become a significant bottleneck during
>> high-frequency file read operations.
>>
>> This patch introduces FOLIO_LOCKED_BIT to distinguish between a
> 
> s/FOLIO_LOCKED_BIT/PAGEREF_LOCKED_BIT/
Ack, thanks

>> (temporary) zero refcount and a locked (dead/frozen) state. Because now
>> incrementing counter doesn't affect it's locked/unlocked state, it is
>> possible to use an optimistic atomic_fetch_add() in
>> page_ref_add_unless_zero() that operates independently of the locked bit.
>> The locked state is handled after the increment attempt, eliminating the
>> need for the CAS loop.
> 
> I don't think I follow.
> 
> Your trick with the PAGEREF_LOCKED_BIT helps with serialization against
> page_ref_freeze(), but I don't think it does anything to serialize
> against freeing the page under you.
> 
> Like, if the page in the process of freeing, page allocator sets its
> refcount to zero and your version of page_ref_add_unless_zero()
> successfully acquirees reference for the freed page.
> 
> How is it safe?

Page is freed only after a successful page_ref_dec_and_test() call, 
which will set LOCKED_BIT. This bit will persist until set_page_count(1) 
is called somewhere in the allocation path [alloc_pages()], and 
effectively block any "use after free" users.

Re: [RFC PATCH 2/2] mm: implement page refcount locking via dedicated bit

[Kiryl Shutsemau]

On Fri, Dec 19, 2025 at 07:18:53PM +0300, Gladyshev Ilya wrote:
> On 12/19/2025 5:50 PM, Kiryl Shutsemau wrote:
> > On Fri, Dec 19, 2025 at 12:46:39PM +0000, Gladyshev Ilya wrote:
> > > The current atomic-based page refcount implementation treats zero
> > > counter as dead and requires a compare-and-swap loop in folio_try_get()
> > > to prevent incrementing a dead refcount. This CAS loop acts as a
> > > serialization point and can become a significant bottleneck during
> > > high-frequency file read operations.
> > > 
> > > This patch introduces FOLIO_LOCKED_BIT to distinguish between a
> > 
> > s/FOLIO_LOCKED_BIT/PAGEREF_LOCKED_BIT/
> Ack, thanks
> 
> > > (temporary) zero refcount and a locked (dead/frozen) state. Because now
> > > incrementing counter doesn't affect it's locked/unlocked state, it is
> > > possible to use an optimistic atomic_fetch_add() in
> > > page_ref_add_unless_zero() that operates independently of the locked bit.
> > > The locked state is handled after the increment attempt, eliminating the
> > > need for the CAS loop.
> > 
> > I don't think I follow.
> > 
> > Your trick with the PAGEREF_LOCKED_BIT helps with serialization against
> > page_ref_freeze(), but I don't think it does anything to serialize
> > against freeing the page under you.
> > 
> > Like, if the page in the process of freeing, page allocator sets its
> > refcount to zero and your version of page_ref_add_unless_zero()
> > successfully acquirees reference for the freed page.
> > 
> > How is it safe?
> 
> Page is freed only after a successful page_ref_dec_and_test() call, which
> will set LOCKED_BIT. This bit will persist until set_page_count(1) is called
> somewhere in the allocation path [alloc_pages()], and effectively block any
> "use after free" users.

Okay, fair enough.

But what prevent the following scenario?

		CPU0					CPU1
page_ref_dec_and_test() 
  atomic_dec_and_test() // refcount=0
					page_ref_add_unless_zero()
					  atomic_add_return() // refcount=1, no LOCKED_BIT
					page_ref_dec_and_test()
					  atomic_dec_and_test() // refcount=0
					  atomic_cmpxchg(0, LOCKED_BIT) // succeeds
  atomic_cmpxchg(0, LOCKED_BIT) // fails
  // return false to caller
// Use-after-free: BOOM!

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [RFC PATCH 2/2] mm: implement page refcount locking via dedicated bit

[Gregory Price]

On Fri, Dec 19, 2025 at 12:46:39PM +0000, Gladyshev Ilya wrote:
> The current atomic-based page refcount implementation treats zero
> counter as dead and requires a compare-and-swap loop in folio_try_get()
> to prevent incrementing a dead refcount. This CAS loop acts as a
> serialization point and can become a significant bottleneck during
> high-frequency file read operations.
> 
> This patch introduces FOLIO_LOCKED_BIT to distinguish between a
> (temporary) zero refcount and a locked (dead/frozen) state. Because now
> incrementing counter doesn't affect it's locked/unlocked state, it is
> possible to use an optimistic atomic_fetch_add() in
> page_ref_add_unless_zero() that operates independently of the locked bit.
> The locked state is handled after the increment attempt, eliminating the
> need for the CAS loop.
>

Such a fundamental change needs additional validation to show there's no
obvious failures.  Have you run this through a model checker to verify
the only failure condition is the 2^31 overflow condition you describe?

A single benchmark and a short changelog is leaves me very uneasy about
such a change.

~Gregory

Re: [RFC PATCH 2/2] mm: implement page refcount locking via dedicated bit

[Gladyshev Ilya]

On 12/19/2025 8:46 PM, Kiryl Shutsemau wrote:
> On Fri, Dec 19, 2025 at 07:18:53PM +0300, Gladyshev Ilya wrote:
>> On 12/19/2025 5:50 PM, Kiryl Shutsemau wrote:
>>> On Fri, Dec 19, 2025 at 12:46:39PM +0000, Gladyshev Ilya wrote:
>>>> The current atomic-based page refcount implementation treats zero
>>>> counter as dead and requires a compare-and-swap loop in folio_try_get()
>>>> to prevent incrementing a dead refcount. This CAS loop acts as a
>>>> serialization point and can become a significant bottleneck during
>>>> high-frequency file read operations.
>>>>
>>>> This patch introduces FOLIO_LOCKED_BIT to distinguish between a
>>>
>>> s/FOLIO_LOCKED_BIT/PAGEREF_LOCKED_BIT/
>> Ack, thanks
>>
>>>> (temporary) zero refcount and a locked (dead/frozen) state. Because now
>>>> incrementing counter doesn't affect it's locked/unlocked state, it is
>>>> possible to use an optimistic atomic_fetch_add() in
>>>> page_ref_add_unless_zero() that operates independently of the locked bit.
>>>> The locked state is handled after the increment attempt, eliminating the
>>>> need for the CAS loop.
>>>
>>> I don't think I follow.
>>>
>>> Your trick with the PAGEREF_LOCKED_BIT helps with serialization against
>>> page_ref_freeze(), but I don't think it does anything to serialize
>>> against freeing the page under you.
>>>
>>> Like, if the page in the process of freeing, page allocator sets its
>>> refcount to zero and your version of page_ref_add_unless_zero()
>>> successfully acquirees reference for the freed page.
>>>
>>> How is it safe?
>>
>> Page is freed only after a successful page_ref_dec_and_test() call, which
>> will set LOCKED_BIT. This bit will persist until set_page_count(1) is called
>> somewhere in the allocation path [alloc_pages()], and effectively block any
>> "use after free" users.
> 
> Okay, fair enough.
> 
> But what prevent the following scenario?
> 
> 		CPU0					CPU1
> page_ref_dec_and_test()
>    atomic_dec_and_test() // refcount=0
> 					page_ref_add_unless_zero()
> 					  atomic_add_return() // refcount=1, no LOCKED_BIT
> 					page_ref_dec_and_test()
> 					  atomic_dec_and_test() // refcount=0
> 					  atomic_cmpxchg(0, LOCKED_BIT) // succeeds
>    atomic_cmpxchg(0, LOCKED_BIT) // fails
>    // return false to caller
> // Use-after-free: BOOM!
> 
But you can't trust that the page is safe to use after 
page_ref_dec_and_test() returns false, if I understood your example 
correctly. For example, current implementation can also lead to this 
'bug' if you slightly change the order of atomic ops in your example:

Initial refcount value: 1 from CPU 0
        CPU 0                                CPU 1
page_ref_and_dec()               page_ref_add_unless_zero()
                                     atomic_add_return() [1 -> 2]
    atomic_dec_and_test() [2 -> 1]
                                  page_ref_dec_and_test()
                                     atomic_dec_and_test() [1 -> 0]
                                  /* page is logically freed here */
    return false [cause 1!=0]
// Caller with use after free?

Re: [RFC PATCH 2/2] mm: implement page refcount locking via dedicated bit

[Gladyshev Ilya]

On 12/19/2025 9:17 PM, Gregory Price wrote:
> On Fri, Dec 19, 2025 at 12:46:39PM +0000, Gladyshev Ilya wrote:
>> The current atomic-based page refcount implementation treats zero
>> counter as dead and requires a compare-and-swap loop in folio_try_get()
>> to prevent incrementing a dead refcount. This CAS loop acts as a
>> serialization point and can become a significant bottleneck during
>> high-frequency file read operations.
>>
>> This patch introduces FOLIO_LOCKED_BIT to distinguish between a
>> (temporary) zero refcount and a locked (dead/frozen) state. Because now
>> incrementing counter doesn't affect it's locked/unlocked state, it is
>> possible to use an optimistic atomic_fetch_add() in
>> page_ref_add_unless_zero() that operates independently of the locked bit.
>> The locked state is handled after the increment attempt, eliminating the
>> need for the CAS loop.
>>
> 
> Such a fundamental change needs additional validation to show there's no
> obvious failures.  Have you run this through a model checker to verify
> the only failure condition is the 2^31 overflow condition you describe?
Aside from extensive logical reasoning, I validated some racy situations 
via tools/memory-model model checking:
1. Increment vs. free race (bad output: use-after-free | memory leak)
2. Free vs. free race (bad output: double free | memory leak)
3. Increment vs. freeze (bad output: both fails)
4. Increment vs. unfreeze (bad output: missed increment)

If there are other scenarios you are concerned about, I will model them 
as well. You can find the litmus tests at the end of this email.
> A single benchmark and a short changelog is leaves me very uneasy about
> such a change.
This RFC submission was primarily focused on demonstrating the concept 
and the performance gain for the reported bottleneck. I will improve the 
changelog (and safety reasoning) for later submissions, as well as the 
benchmarking side.

---

Note: I used 32 as locked bit in model tests for better readability. It 
doesn't affect anything

---

diff --git 
a/tools/memory-model/litmus-tests/folio_refcount/free_free_race.litmus 
b/tools/memory-model/litmus-tests/folio_refcount/free_free_race.litmus
new file mode 100644
index 000000000000..4dc7e899245b
--- /dev/null
+++ b/tools/memory-model/litmus-tests/folio_refcount/free_free_race.litmus
@@ -0,0 +1,37 @@
+C free_vs_free_race
+
+(* Result: Never
+ *
+ * Both P0 and P1 tries to decrement refcount.
+ *
+ * Expected result: only one deallocation (r0 xor r1 == 1)
+ * which is equal to r0 != r1 => bad result is r0 == r1
+*)
+
+{
+       int refcount = 2;
+}
+
+P0(int *refcount)
+{
+       int r0;
+
+       r0 = atomic_dec_and_test(refcount);
+       if (r0) {
+               r0 = atomic_cmpxchg_relaxed(refcount, 0, 32) == 0;
+       }
+}
+
+
+P1(int *refcount)
+{
+       int r1;
+
+       r1 = atomic_dec_and_test(refcount);
+       if (r1) {
+               r1 = atomic_cmpxchg_relaxed(refcount, 0, 32) == 0;
+       }
+}
+
+exists (0:r0 == 1:r1)
+
diff --git 
a/tools/memory-model/litmus-tests/folio_refcount/inc_free_race.litmus 
b/tools/memory-model/litmus-tests/folio_refcount/inc_free_race.litmus
new file mode 100644
index 000000000000..863abba48415
--- /dev/null
+++ b/tools/memory-model/litmus-tests/folio_refcount/inc_free_race.litmus
@@ -0,0 +1,34 @@
+C inc_free_race
+
+(* Result: Never
+ *
+ * P0 tries to decrement free object.
+ * P1 tries to acquire it.
+ * Expected result: one of them failes (r0 xor r1 == 1),
+ *   so bad result is r0 == r1
+*)
+
+{
+       int refcount = 1;
+}
+
+P0(int *refcount)
+{
+       int r0;
+
+       r0 = atomic_dec_and_test(refcount);
+       if (r0) {
+               r0 = atomic_cmpxchg_relaxed(refcount, 0, 32) == 0;
+       }
+}
+
+
+P1(int *refcount)
+{
+       int r1;
+
+       r1 = atomic_add_return(1, refcount);
+       r1 = (r1 & (32)) == 0;
+}
+
+exists (0:r0 == 1:r1)
diff --git 
a/tools/memory-model/litmus-tests/folio_refcount/inc_freeze_race.litmus 
b/tools/memory-model/litmus-tests/folio_refcount/inc_freeze_race.litmus
new file mode 100644
index 000000000000..6e3a4112080c
--- /dev/null
+++ b/tools/memory-model/litmus-tests/folio_refcount/inc_freeze_race.litmus
@@ -0,0 +1,31 @@
+C inc_freeze_race
+
+(* Result: Never
+ *
+ * P0 tries to freeze counter with value 3 (can be arbitary).
+ * P1 tries to acquire reference.
+ * Expected result: one of them failes (r0 xor r1 == 1),
+ *   so bad result is r0 == r1 (= 0, 1).
+*)
+
+{
+       int refcount = 3;
+}
+
+P0(int *refcount)
+{
+       int r0;
+
+       r0 = atomic_cmpxchg(refcount, 3, 32);
+}
+
+
+P1(int *refcount)
+{
+       int r0;
+
+       r0 = atomic_add_return(1, refcount);
+       r0 = (r0 & (32)) == 0;
+}
+
+exists (0:r0 == 1:r0)
diff --git 
a/tools/memory-model/litmus-tests/folio_refcount/inc_unfreeze_race.litmus 
b/tools/memory-model/litmus-tests/folio_refcount/inc_unfreeze_race.litmus
new file mode 100644
index 000000000000..f7e2273fe7da
--- /dev/null
+++ 
b/tools/memory-model/litmus-tests/folio_refcount/inc_unfreeze_race.litmus
@@ -0,0 +1,30 @@
+C inc_unfreeze_race
+
+(* Result: Never
+ *
+ * P0 tries to unfreeze refcount with saved value 3
+ * P1 tries to acquire reference.
+ *
+ * Expected result: P1 fails or in the end refcount is 4
+ * Bad result: Missed refcount
+*)
+
+{
+       int refcount = 32;
+}
+
+P0(int *refcount)
+{
+       smp_store_release(refcount, 3);
+}
+
+
+P1(int *refcount)
+{
+       int r0;
+
+       r0 = atomic_add_return(1, refcount);
+       r0 = (r0 & (32)) == 0;
+}
+
+exists (1:r0=1 /\ refcount != 4)

Re: [RFC PATCH 2/2] mm: implement page refcount locking via dedicated bit

[Kiryl Shutsemau]

On Fri, Dec 19, 2025 at 10:08:54PM +0300, Gladyshev Ilya wrote:
> On 12/19/2025 8:46 PM, Kiryl Shutsemau wrote:
> > On Fri, Dec 19, 2025 at 07:18:53PM +0300, Gladyshev Ilya wrote:
> > > On 12/19/2025 5:50 PM, Kiryl Shutsemau wrote:
> > > > On Fri, Dec 19, 2025 at 12:46:39PM +0000, Gladyshev Ilya wrote:
> > > > > The current atomic-based page refcount implementation treats zero
> > > > > counter as dead and requires a compare-and-swap loop in folio_try_get()
> > > > > to prevent incrementing a dead refcount. This CAS loop acts as a
> > > > > serialization point and can become a significant bottleneck during
> > > > > high-frequency file read operations.
> > > > > 
> > > > > This patch introduces FOLIO_LOCKED_BIT to distinguish between a
> > > > 
> > > > s/FOLIO_LOCKED_BIT/PAGEREF_LOCKED_BIT/
> > > Ack, thanks
> > > 
> > > > > (temporary) zero refcount and a locked (dead/frozen) state. Because now
> > > > > incrementing counter doesn't affect it's locked/unlocked state, it is
> > > > > possible to use an optimistic atomic_fetch_add() in
> > > > > page_ref_add_unless_zero() that operates independently of the locked bit.
> > > > > The locked state is handled after the increment attempt, eliminating the
> > > > > need for the CAS loop.
> > > > 
> > > > I don't think I follow.
> > > > 
> > > > Your trick with the PAGEREF_LOCKED_BIT helps with serialization against
> > > > page_ref_freeze(), but I don't think it does anything to serialize
> > > > against freeing the page under you.
> > > > 
> > > > Like, if the page in the process of freeing, page allocator sets its
> > > > refcount to zero and your version of page_ref_add_unless_zero()
> > > > successfully acquirees reference for the freed page.
> > > > 
> > > > How is it safe?
> > > 
> > > Page is freed only after a successful page_ref_dec_and_test() call, which
> > > will set LOCKED_BIT. This bit will persist until set_page_count(1) is called
> > > somewhere in the allocation path [alloc_pages()], and effectively block any
> > > "use after free" users.
> > 
> > Okay, fair enough.
> > 
> > But what prevent the following scenario?
> > 
> > 		CPU0					CPU1
> > page_ref_dec_and_test()
> >    atomic_dec_and_test() // refcount=0
> > 					page_ref_add_unless_zero()
> > 					  atomic_add_return() // refcount=1, no LOCKED_BIT
> > 					page_ref_dec_and_test()
> > 					  atomic_dec_and_test() // refcount=0
> > 					  atomic_cmpxchg(0, LOCKED_BIT) // succeeds
> >    atomic_cmpxchg(0, LOCKED_BIT) // fails
> >    // return false to caller
> > // Use-after-free: BOOM!
> > 
> But you can't trust that the page is safe to use after
> page_ref_dec_and_test() returns false, if I understood your example
> correctly.

True. My bad.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [RFC PATCH 2/2] mm: implement page refcount locking via dedicated bit

[kernel test robot]

Hi Gladyshev,

[This is a private test report for your RFC patch.]
kernel test robot noticed the following build warnings:

[auto build test WARNING on akpm-mm/mm-everything]

url:    https://github.com/intel-lab-lkp/linux/commits/Gladyshev-Ilya/mm-make-ref_unless-functions-unless_zero-only/20251219-204741
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/81e3c45f49bdac231e831ec7ba09ef42fbb77930.1766145604.git.gladyshev.ilya1%40h-partners.com
patch subject: [RFC PATCH 2/2] mm: implement page refcount locking via dedicated bit
config: sparc64-randconfig-r121-20251223 (https://download.01.org/0day-ci/archive/20251223/202512230743.ghGC9zn7-lkp@intel.com/config)
compiler: clang version 22.0.0git (https://github.com/llvm/llvm-project 185f5fd5ce4c65116ca8cf6df467a682ef090499)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251223/202512230743.ghGC9zn7-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202512230743.ghGC9zn7-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
   fs/pipe.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/splice.c:55:19: sparse: sparse: cast from restricted fmode_t
   fs/splice.c:55:19: sparse: sparse: cast from restricted fmode_t
   fs/splice.c:55:19: sparse: sparse: cast to restricted fmode_t
   fs/splice.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/exec.c:311:39: sparse: sparse: incorrect type in return expression (different address spaces) @@     expected char const [noderef] __user * @@     got void * @@
   fs/exec.c:311:39: sparse:     expected char const [noderef] __user *
   fs/exec.c:311:39: sparse:     got void *
   fs/exec.c:318:31: sparse: sparse: incorrect type in return expression (different address spaces) @@     expected char const [noderef] __user * @@     got void * @@
   fs/exec.c:318:31: sparse:     expected char const [noderef] __user *
   fs/exec.c:318:31: sparse:     got void *
   fs/exec.c:911:48: sparse: sparse: incorrect type in initializer (different address spaces) @@     expected struct sighand_struct *oldsighand @@     got struct sighand_struct [noderef] __rcu *sighand @@
   fs/exec.c:911:48: sparse:     expected struct sighand_struct *oldsighand
   fs/exec.c:911:48: sparse:     got struct sighand_struct [noderef] __rcu *sighand
   fs/exec.c:1017:56: sparse: sparse: incorrect type in argument 2 (different address spaces) @@     expected struct task_struct *parent @@     got struct task_struct [noderef] __rcu *parent @@
   fs/exec.c:1017:56: sparse:     expected struct task_struct *parent
   fs/exec.c:1017:56: sparse:     got struct task_struct [noderef] __rcu *parent
   fs/exec.c:1052:47: sparse: sparse: incorrect type in initializer (different address spaces) @@     expected struct sighand_struct *oldsighand @@     got struct sighand_struct [noderef] __rcu *sighand @@
   fs/exec.c:1052:47: sparse:     expected struct sighand_struct *oldsighand
   fs/exec.c:1052:47: sparse:     got struct sighand_struct [noderef] __rcu *sighand
   fs/exec.c:1167:26: sparse: sparse: incorrect type in argument 1 (different address spaces) @@     expected struct spinlock [usertype] *lock @@     got struct spinlock [noderef] __rcu * @@
   fs/exec.c:1167:26: sparse:     expected struct spinlock [usertype] *lock
   fs/exec.c:1167:26: sparse:     got struct spinlock [noderef] __rcu *
   fs/exec.c:1169:28: sparse: sparse: incorrect type in argument 1 (different address spaces) @@     expected struct spinlock [usertype] *lock @@     got struct spinlock [noderef] __rcu * @@
   fs/exec.c:1169:28: sparse:     expected struct spinlock [usertype] *lock
   fs/exec.c:1169:28: sparse:     got struct spinlock [noderef] __rcu *
   fs/exec.c:1692:70: sparse: sparse: incorrect type in argument 1 (different address spaces) @@     expected struct task_struct *tsk @@     got struct task_struct [noderef] __rcu *parent @@
   fs/exec.c:1692:70: sparse:     expected struct task_struct *tsk
   fs/exec.c:1692:70: sparse:     got struct task_struct [noderef] __rcu *parent
   fs/exec.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/libfs.c:2170:18: sparse: sparse: incompatible types in comparison expression (different address spaces):
   fs/libfs.c:2170:18: sparse:    struct dentry [noderef] __rcu *
   fs/libfs.c:2170:18: sparse:    struct dentry *
   fs/libfs.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/mpage.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/remap_range.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/namei.c:779:13: sparse: sparse: context imbalance in 'leave_rcu' - unexpected unlock
   fs/namei.c:2610:19: sparse: sparse: context imbalance in 'path_init' - different lock contexts for basic block
   fs/namei.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/aio.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
   fs/aio.c:1687:13: sparse: sparse: context imbalance in 'poll_iocb_lock_wq' - different lock contexts for basic block
   fs/aio.c:1718:13: sparse: sparse: context imbalance in 'poll_iocb_unlock_wq' - unexpected unlock
--
   fs/buffer.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
   fs/buffer.c:251:18: sparse: sparse: context imbalance in '__find_get_block_slow' - different lock contexts for basic block
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/coredump.c:508:27: sparse: sparse: incorrect type in argument 1 (different address spaces) @@     expected struct spinlock [usertype] *lock @@     got struct spinlock [noderef] __rcu * @@
   fs/coredump.c:508:27: sparse:     expected struct spinlock [usertype] *lock
   fs/coredump.c:508:27: sparse:     got struct spinlock [noderef] __rcu *
   fs/coredump.c:517:29: sparse: sparse: incorrect type in argument 1 (different address spaces) @@     expected struct spinlock [usertype] *lock @@     got struct spinlock [noderef] __rcu * @@
   fs/coredump.c:517:29: sparse:     expected struct spinlock [usertype] *lock
   fs/coredump.c:517:29: sparse:     got struct spinlock [noderef] __rcu *
   fs/coredump.c:556:31: sparse: sparse: incorrect type in argument 1 (different address spaces) @@     expected struct spinlock [usertype] *lock @@     got struct spinlock [noderef] __rcu * @@
   fs/coredump.c:556:31: sparse:     expected struct spinlock [usertype] *lock
   fs/coredump.c:556:31: sparse:     got struct spinlock [noderef] __rcu *
   fs/coredump.c:561:33: sparse: sparse: incorrect type in argument 1 (different address spaces) @@     expected struct spinlock [usertype] *lock @@     got struct spinlock [noderef] __rcu * @@
   fs/coredump.c:561:33: sparse:     expected struct spinlock [usertype] *lock
   fs/coredump.c:561:33: sparse:     got struct spinlock [noderef] __rcu *
   fs/coredump.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/verity/read_metadata.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/verity/verify.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/iomap/buffered-io.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/ext4/inline.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/ext4/inode.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/ext4/move_extent.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/ext4/readpage.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/ext4/verity.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/ext2/dir.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/ext2/namei.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/jbd2/commit.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/minix/namei.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/minix/dir.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/hfsplus/btree.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/hfsplus/bnode.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/hfsplus/xattr.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/hfs/bnode.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/hfs/btree.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/ecryptfs/mmap.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/ecryptfs/read_write.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/freevxfs/vxfs_lookup.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/ntfs3/attrib.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/ntfs3/fsntfs.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/ntfs3/frecord.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/ntfs3/file.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/ntfs3/inode.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/ufs/balloc.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/ufs/dir.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/ufs/inode.c: note: in included file:
   fs/ufs/util.h:192:40: sparse: sparse: restricted __fs16 degrades to integer
   fs/ufs/util.h:226:40: sparse: sparse: restricted __fs16 degrades to integer
   fs/ufs/inode.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/ufs/namei.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/ufs/util.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/jffs2/file.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/jffs2/gc.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/ubifs/file.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/affs/file.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/qnx6/dir.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/fuse/file.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/fuse/readdir.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/fuse/ioctl.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/orangefs/inode.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/udf/inode.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/udf/symlink.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/nilfs2/dir.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/nilfs2/namei.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/nilfs2/page.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/nilfs2/mdt.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/nilfs2/btnode.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/nilfs2/recovery.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/nilfs2/gcinode.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/gfs2/bmap.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
   fs/gfs2/bmap.c:1683:42: sparse: sparse: unsigned value that used to be signed checked against zero?
   fs/gfs2/bmap.c:1981:16: sparse: signed value source
--
   fs/gfs2/lops.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/gfs2/meta_io.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/gfs2/aops.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/f2fs/dir.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/f2fs/inode.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/f2fs/file.c:3705:36: sparse: sparse: incorrect type in argument 1 (different base types) @@     expected unsigned short const [usertype] *pwcs @@     got restricted __le16 * @@
   fs/f2fs/file.c:3705:36: sparse:     expected unsigned short const [usertype] *pwcs
   fs/f2fs/file.c:3705:36: sparse:     got restricted __le16 *
   fs/f2fs/file.c:3741:28: sparse: sparse: incorrect type in argument 4 (different base types) @@     expected unsigned short [usertype] *pwcs @@     got restricted __le16 * @@
   fs/f2fs/file.c:3741:28: sparse:     expected unsigned short [usertype] *pwcs
   fs/f2fs/file.c:3741:28: sparse:     got restricted __le16 *
   fs/f2fs/file.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/f2fs/namei.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/f2fs/inline.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/f2fs/checkpoint.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/f2fs/gc.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/f2fs/recovery.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/f2fs/node.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/f2fs/verity.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/f2fs/xattr.c:844:1: sparse: sparse: no newline at end of file
   fs/f2fs/xattr.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/f2fs/data.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/f2fs/segment.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/erofs/data.c:263:26: sparse: sparse: Using plain integer as NULL pointer
   fs/erofs/data.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/erofs/fileio.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
--
   fs/erofs/zdata.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
   fs/erofs/zdata.c:954:32: sparse: sparse: context imbalance in 'z_erofs_put_pcluster' - different lock contexts for basic block
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)
>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffff80000000 becomes 0)

vim +161 arch/sparc/include/asm/cmpxchg_64.h

d550bbd40c0e10 David Howells 2012-03-28  155  
d550bbd40c0e10 David Howells 2012-03-28  156  static inline unsigned long
d550bbd40c0e10 David Howells 2012-03-28  157  __cmpxchg(volatile void *ptr, unsigned long old, unsigned long new, int size)
d550bbd40c0e10 David Howells 2012-03-28  158  {
d550bbd40c0e10 David Howells 2012-03-28  159  	switch (size) {
a12ee2349312d7 Babu Moger    2017-05-24  160  		case 1:
a12ee2349312d7 Babu Moger    2017-05-24 @161  			return __cmpxchg_u8(ptr, old, new);
d550bbd40c0e10 David Howells 2012-03-28  162  		case 4:
d550bbd40c0e10 David Howells 2012-03-28  163  			return __cmpxchg_u32(ptr, old, new);
d550bbd40c0e10 David Howells 2012-03-28  164  		case 8:
d550bbd40c0e10 David Howells 2012-03-28  165  			return __cmpxchg_u64(ptr, old, new);
d550bbd40c0e10 David Howells 2012-03-28  166  	}
d550bbd40c0e10 David Howells 2012-03-28  167  	__cmpxchg_called_with_bad_pointer();
d550bbd40c0e10 David Howells 2012-03-28  168  	return old;
d550bbd40c0e10 David Howells 2012-03-28  169  }
d550bbd40c0e10 David Howells 2012-03-28  170  

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [RFC PATCH 0/2] mm: improve folio refcount scalability

[Gladyshev Ilya]

Gentle ping on this proposal

> Intro
> =====
> This patch optimizes small file read performance and overall folio refcount
> scalability by refactoring page_ref_add_unless [core of folio_try_get].
> This is alternative approach to previous attempts to fix small read
> performance by avoiding refcount bumps [1][2].
> 
> Overview
> ========
> Current refcount implementation is using zero counter as locked (dead/frozen)
> state, which required CAS loop for increments to avoid temporary unlocks in
> try_get functions. These CAS loops became a serialization point for otherwise
> scalable and fast read side.
> 
> Proposed implementation separates "locked" logic from the counting, allowing
> the use of optimistic fetch_add() instead of CAS. For more details, please
> refer to the commit message of the patch itself.
> 
> Proposed logic maintains the same public API as before, including all existing
> memory barrier guarantees.
> 
> Drawbacks
> =========
> In theory, an optimistic fetch_add can overflow the atomic_t and reset the
> locked state. Currently, this is mitigated via a single CAS operation after
> the "failed" fetch_add, which tries to reset the counter to a locked zero.
> While this best-effort approach doesn't have any strong guarantees, it's
> unrealistic that there will be 2^31 highly contended try_get calls on a locked
> folio, and in each of these calls, the CAS operation will fail.
> 
> If this guarantee isn't sufficient, it can be improved by performing a full
> CAS loop when the counter is approaching overflow.
> 
> Performance
> ===========
> Performance was measured using a simple custom benchmark based on
> will-it-scale[3]. This benchmark spawns N pinned threads/processes that
> execute the following loop:
> ``
> char buf[]
> fd = open(/* same file in tmpfs */);
> 
> while (true) {
>      pread(fd, buf, /* read size = */ 64, /* offset = */0)
> }
> ``
> While this is a synthetic load, it does highlight existing issue and
> doesn't differ a lot from benchmarking in [2] patch.
> 
> This benchmark measures operations per second in the inner loop and the
> results across all workers. Performance was tested on top of v6.15 kernel[4]
> on two platforms. Since threads and processes showed similar performance on
> both systems, only the thread results are provided below. The performance
> improvement scales linearly between the CPU counts shown.
> 
> Platform 1: 2 x E5-2690 v3, 12C/12T each [disabled SMT]
> 
> #threads | vanilla | patched | boost (%)
>         1 | 1343381 | 1344401 |  +0.1
>         2 | 2186160 | 2455837 | +12.3
>         5 | 5277092 | 6108030 | +15.7
>        10 | 5858123 | 7506328 | +28.1
>        12 | 6484445 | 8137706 | +25.5
>           /* Cross socket NUMA */
>        14 | 3145860 | 4247391 | +35.0
>        16 | 2350840 | 4262707 | +81.3
>        18 | 2378825 | 4121415 | +73.2
>        20 | 2438475 | 4683548 | +92.1
>        24 | 2325998 | 4529737 | +94.7
> 
> Platform 2: 2 x AMD EPYC 9654, 96C/192T each [enabled SMT]
> 
> #threads | vanilla | patched | boost (%)
>         1 | 1077276 | 1081653 |  +0.4
>         5 | 4286838 | 4682513 |  +9.2
>        10 | 1698095 | 1902753 | +12.1
>        20 | 1662266 | 1921603 | +15.6
>        49 | 1486745 | 1828926 | +23.0
>        97 | 1617365 | 2052635 | +26.9
>           /* Cross socket NUMA */
>       105 | 1368319 | 1798862 | +31.5
>       136 | 1008071 | 1393055 | +38.2
>       168 |  879332 | 1245210 | +41.6
>                 /* SMT */
>       193 |  905432 | 1294833 | +43.0
>       289 |  851988 | 1313110 | +54.1
>       353 |  771288 | 1347165 | +74.7
> 
> [1] https://lore.kernel.org/linux-mm/CAHk-=wj00-nGmXEkxY=-=Z_qP6kiGUziSFvxHJ9N-cLWry5zpA@mail.gmail.com/
> [2] https://lore.kernel.org/linux-mm/20251017141536.577466-1-kirill@shutemov.name/
> [3] https://github.com/antonblanchard/will-it-scale
> [4] There were no changes to page_ref.h between v6.15 and v6.18 or any
>      significant performance changes on the read side in mm/filemap.c
> 
> Gladyshev Ilya (2):
>    mm: make ref_unless functions unless_zero only
>    mm: implement page refcount locking via dedicated bit
> 
>   include/linux/mm.h         |  2 +-
>   include/linux/page-flags.h |  9 ++++++---
>   include/linux/page_ref.h   | 35 ++++++++++++++++++++++++++---------
>   3 files changed, 33 insertions(+), 13 deletions(-)
> 

Re: [RFC PATCH 0/2] mm: improve folio refcount scalability

[Kiryl Shutsemau]

On Mon, Jan 12, 2026 at 11:30:38AM +0300, Gladyshev Ilya wrote:
> Gentle ping on this proposal

I generally like the idea, but I would like to hear from folks who
actually understand serialization.

Also, do you have number for "a full CAS loop when the counter is
approaching overflow" thing?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [RFC PATCH 0/2] mm: improve folio refcount scalability

[Gladyshev Ilya]

On 1/12/2026 2:49 PM, Kiryl Shutsemau wrote:
> On Mon, Jan 12, 2026 at 11:30:38AM +0300, Gladyshev Ilya wrote:
>> Gentle ping on this proposal
> 
> I generally like the idea, but I would like to hear from folks who
> actually understand serialization.
> 
> Also, do you have number for "a full CAS loop when the counter is
> approaching overflow" thing?
> 
I am not sure that overflow is a real problem because you need a very 
specific race condition over a long time to achieve it... But as a 
safeguard, everything lower than 2^31 - #max concurrent accesses (~#num 
cpu) should work, so let's say 2^30

Re: [RFC PATCH 0/2] mm: improve folio refcount scalability

[Kiryl Shutsemau]

On Mon, Jan 12, 2026 at 05:32:10PM +0300, Gladyshev Ilya wrote:
> On 1/12/2026 2:49 PM, Kiryl Shutsemau wrote:
> > On Mon, Jan 12, 2026 at 11:30:38AM +0300, Gladyshev Ilya wrote:
> > > Gentle ping on this proposal
> > 
> > I generally like the idea, but I would like to hear from folks who
> > actually understand serialization.
> > 
> > Also, do you have number for "a full CAS loop when the counter is
> > approaching overflow" thing?
> > 
> I am not sure that overflow is a real problem because you need a very
> specific race condition over a long time to achieve it...

Yes. But if the page is popular for pinning, GUP_PIN_COUNTING_BIAS can
cut the "very long time" substantially.

> But as a safeguard, everything lower than 2^31 - #max concurrent
> accesses (~#num cpu) should work, so let's say 2^30

What I meant is when we put a branch/loop in the hot path, your
performance numbers will likely not look as attractive. Am I wrong?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [RFC PATCH 0/2] mm: improve folio refcount scalability

[Gladyshev Ilya]

On 1/12/2026 7:17 PM, Kiryl Shutsemau wrote:
> On Mon, Jan 12, 2026 at 05:32:10PM +0300, Gladyshev Ilya wrote:
>> On 1/12/2026 2:49 PM, Kiryl Shutsemau wrote:
>>> On Mon, Jan 12, 2026 at 11:30:38AM +0300, Gladyshev Ilya wrote:
>>>> Gentle ping on this proposal
>>>
>>> I generally like the idea, but I would like to hear from folks who
>>> actually understand serialization.
>>>
>>> Also, do you have number for "a full CAS loop when the counter is
>>> approaching overflow" thing?
>>>
>> I am not sure that overflow is a real problem because you need a very
>> specific race condition over a long time to achieve it...
> 
> Yes. But if the page is popular for pinning, GUP_PIN_COUNTING_BIAS can
> cut the "very long time" substantially.
> 
>> But as a safeguard, everything lower than 2^31 - #max concurrent
>> accesses (~#num cpu) should work, so let's say 2^30
> 
> What I meant is when we put a branch/loop in the hot path, your
> performance numbers will likely not look as attractive. Am I wrong?
> 
It would be under the same branch as the single CAS that already exists 
in this patch:

   if (page_count_writable(page)) {
     val = atomic_add_return(nr, &page->_refcount);
     ret = !(val & PAGEREF_LOCKED_BIT);

     if (unlikely(!ret)) {
       atomic_cmpxchg_relaxed(&page->_refcount, val, PAGEREF_LOCKED_BIT);
       /* [Proposed] if (failed && big enough) { CAS loop } */
     }		
   }

Unless the "failed try_lock()" is the hot path somewhere[1], this added 
branch will be hidden under the already existing [unlikely taken] branch

[1]: Which I doubt, because failed try_lock() usually includes heavy 
re-lookup

Re: [RFC PATCH 1/2] mm: make ref_unless functions unless_zero only

[David Hildenbrand (Arm)]

On 12/19/25 13:46, Gladyshev Ilya wrote:
> There are no users of (folio/page)_ref_add_unless(page, nr, u) with
> u != 0 [1] and all current users are "internal" for page refcounting API.
> This allows us to safely drop this parameter and reduce function
> semantics to the "unless zero" cases only, which will be optimized in
> the following patch.
> 
> If needed, these functions for the u!=0 cases can be trivially
> reintroduced later using the same atomic_add_unless operations as before.
> 
> [1]: The last user was dropped in v5.18 kernel, commit 27674ef6c73f
> ("mm: remove the extra ZONE_DEVICE struct page refcount"). There is no
> trace of discussion as to why this cleanup wasn't done earlier.
> 
> Co-developed-by: Gorbunov Ivan <gorbunov.ivan@h-partners.com>
> Signed-off-by: Gorbunov Ivan <gorbunov.ivan@h-partners.com>
> Signed-off-by: Gladyshev Ilya <gladyshev.ilya1@h-partners.com>
> ---

This one makes a lot of sense even without #2. Can you send that out 
early as a standalone patch?

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David