* Re: [PATCH v2 2/2] mm: Optimize mremap() by PTE batching
2025-05-07 6:02 ` [PATCH v2 2/2] mm: Optimize mremap() by PTE batching Dev Jain
@ 2025-05-08 1:37 ` Andrew Morton
2025-05-08 4:53 ` Lorenzo Stoakes
2025-05-08 2:00 ` Zi Yan
` (2 subsequent siblings)
3 siblings, 1 reply; 23+ messages in thread
From: Andrew Morton @ 2025-05-08 1:37 UTC (permalink / raw)
To: Dev Jain
Cc: Liam.Howlett, lorenzo.stoakes, vbabka, jannh, pfalcato, linux-mm,
linux-kernel, david, peterx, ryan.roberts, mingo, libang.li,
maobibo, zhengqi.arch, baohua, anshuman.khandual, willy,
ioworker0, yang, baolin.wang, ziy, hughd
On Wed, 7 May 2025 11:32:56 +0530 Dev Jain <dev.jain@arm.com> wrote:
> To use PTE batching, we want to determine whether the folio mapped by
> the PTE is large, thus requiring the use of vm_normal_folio(). We want
> to avoid the cost of vm_normal_folio() if the code path doesn't already
> require the folio. For arm64, pte_batch_hint() does the job. To generalize
> this hint, add a helper which will determine whether two consecutive PTEs
> point to consecutive PFNs, in which case there is a high probability that
> the underlying folio is large.
> Next, use folio_pte_batch() to optimize move_ptes(). On arm64, if the ptes
> are painted with the contig bit, then ptep_get() will iterate through all 16
> entries to collect a/d bits. Hence this optimization will result in a 16x
> reduction in the number of ptep_get() calls. Next, ptep_get_and_clear()
> will eventually call contpte_try_unfold() on every contig block, thus
> flushing the TLB for the complete large folio range. Instead, use
> get_and_clear_full_ptes() so as to elide TLBIs on each contig block, and only
> do them on the starting and ending contig block.
>
> ...
>
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -369,6 +369,35 @@ static inline pgd_t pgdp_get(pgd_t *pgdp)
> }
> #endif
>
> +/**
> + * maybe_contiguous_pte_pfns - Hint whether the page mapped by the pte belongs
> + * to a large folio.
> + * @ptep: Pointer to the page table entry.
> + * @pte: The page table entry.
> + *
> + * This helper is invoked when the caller wants to batch over a set of ptes
> + * mapping a large folio, but the concerned code path does not already have
> + * the folio. We want to avoid the cost of vm_normal_folio() only to find that
> + * the underlying folio was small; i.e keep the small folio case as fast as
> + * possible.
> + *
> + * The caller must ensure that ptep + 1 exists.
> + */
Gee, that isn't the prettiest interface we've ever invented.
Is there any prospect that this function will get another caller? If
not then it's probably better to just open-code all this in the caller
and fill it up with comments.
Anyway, review of this series is scanty. I'd normally enter
wait-and-see mode, but this:
> the average execution time reduces from 1.9 to
> 1.2 seconds, giving a 37% performance optimization, on Apple M3 (arm64).
prompts me into push-it-along mode.
^ permalink raw reply [flat|nested] 23+ messages in thread* Re: [PATCH v2 2/2] mm: Optimize mremap() by PTE batching
2025-05-08 1:37 ` Andrew Morton
@ 2025-05-08 4:53 ` Lorenzo Stoakes
0 siblings, 0 replies; 23+ messages in thread
From: Lorenzo Stoakes @ 2025-05-08 4:53 UTC (permalink / raw)
To: Andrew Morton
Cc: Dev Jain, Liam.Howlett, vbabka, jannh, pfalcato, linux-mm,
linux-kernel, david, peterx, ryan.roberts, mingo, libang.li,
maobibo, zhengqi.arch, baohua, anshuman.khandual, willy,
ioworker0, yang, baolin.wang, ziy, hughd
On Wed, May 07, 2025 at 06:37:03PM -0700, Andrew Morton wrote:
> On Wed, 7 May 2025 11:32:56 +0530 Dev Jain <dev.jain@arm.com> wrote:
>
> > To use PTE batching, we want to determine whether the folio mapped by
> > the PTE is large, thus requiring the use of vm_normal_folio(). We want
> > to avoid the cost of vm_normal_folio() if the code path doesn't already
> > require the folio. For arm64, pte_batch_hint() does the job. To generalize
> > this hint, add a helper which will determine whether two consecutive PTEs
> > point to consecutive PFNs, in which case there is a high probability that
> > the underlying folio is large.
> > Next, use folio_pte_batch() to optimize move_ptes(). On arm64, if the ptes
> > are painted with the contig bit, then ptep_get() will iterate through all 16
> > entries to collect a/d bits. Hence this optimization will result in a 16x
> > reduction in the number of ptep_get() calls. Next, ptep_get_and_clear()
> > will eventually call contpte_try_unfold() on every contig block, thus
> > flushing the TLB for the complete large folio range. Instead, use
> > get_and_clear_full_ptes() so as to elide TLBIs on each contig block, and only
> > do them on the starting and ending contig block.
> >
> > ...
> >
> > --- a/include/linux/pgtable.h
> > +++ b/include/linux/pgtable.h
> > @@ -369,6 +369,35 @@ static inline pgd_t pgdp_get(pgd_t *pgdp)
> > }
> > #endif
> >
> > +/**
> > + * maybe_contiguous_pte_pfns - Hint whether the page mapped by the pte belongs
> > + * to a large folio.
> > + * @ptep: Pointer to the page table entry.
> > + * @pte: The page table entry.
> > + *
> > + * This helper is invoked when the caller wants to batch over a set of ptes
> > + * mapping a large folio, but the concerned code path does not already have
> > + * the folio. We want to avoid the cost of vm_normal_folio() only to find that
> > + * the underlying folio was small; i.e keep the small folio case as fast as
> > + * possible.
> > + *
> > + * The caller must ensure that ptep + 1 exists.
> > + */
>
> Gee, that isn't the prettiest interface we've ever invented.
>
> Is there any prospect that this function will get another caller? If
> not then it's probably better to just open-code all this in the caller
> and fill it up with comments.
>
>
> Anyway, review of this series is scanty. I'd normally enter
> wait-and-see mode, but this:
>
> > the average execution time reduces from 1.9 to
> > 1.2 seconds, giving a 37% performance optimization, on Apple M3 (arm64).
>
> prompts me into push-it-along mode.
>
>
There's been a ton of review on the v1 (see [0]), I will get to this one
soon, but as you can see from the v1 review there's lots we need to check
for correctness.
So it's coming :)
[0]: https://lore.kernel.org/linux-mm/20250506050056.59250-1-dev.jain@arm.com/
Let's not be too hasty to merge this though until we're sure it's safe
(this is delicate code). But I'll be giving R-b tags on a finalised version
anyway.
^ permalink raw reply [flat|nested] 23+ messages in thread
* Re: [PATCH v2 2/2] mm: Optimize mremap() by PTE batching
2025-05-07 6:02 ` [PATCH v2 2/2] mm: Optimize mremap() by PTE batching Dev Jain
2025-05-08 1:37 ` Andrew Morton
@ 2025-05-08 2:00 ` Zi Yan
2025-05-08 4:01 ` Dev Jain
2025-05-08 6:31 ` Anshuman Khandual
2025-05-08 7:16 ` Anshuman Khandual
2025-05-08 10:04 ` Lorenzo Stoakes
3 siblings, 2 replies; 23+ messages in thread
From: Zi Yan @ 2025-05-08 2:00 UTC (permalink / raw)
To: Dev Jain
Cc: akpm, Liam.Howlett, lorenzo.stoakes, vbabka, jannh, pfalcato,
linux-mm, linux-kernel, david, peterx, ryan.roberts, mingo,
libang.li, maobibo, zhengqi.arch, baohua, anshuman.khandual,
willy, ioworker0, yang, baolin.wang, hughd
On 7 May 2025, at 2:02, Dev Jain wrote:
> To use PTE batching, we want to determine whether the folio mapped by
> the PTE is large, thus requiring the use of vm_normal_folio(). We want
> to avoid the cost of vm_normal_folio() if the code path doesn't already
> require the folio. For arm64, pte_batch_hint() does the job. To generalize
> this hint, add a helper which will determine whether two consecutive PTEs
> point to consecutive PFNs, in which case there is a high probability that
> the underlying folio is large.
> Next, use folio_pte_batch() to optimize move_ptes(). On arm64, if the ptes
> are painted with the contig bit, then ptep_get() will iterate through all 16
> entries to collect a/d bits. Hence this optimization will result in a 16x
> reduction in the number of ptep_get() calls. Next, ptep_get_and_clear()
> will eventually call contpte_try_unfold() on every contig block, thus
> flushing the TLB for the complete large folio range. Instead, use
> get_and_clear_full_ptes() so as to elide TLBIs on each contig block, and only
> do them on the starting and ending contig block.
>
> Signed-off-by: Dev Jain <dev.jain@arm.com>
> ---
> include/linux/pgtable.h | 29 +++++++++++++++++++++++++++++
> mm/mremap.c | 37 ++++++++++++++++++++++++++++++-------
> 2 files changed, 59 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index b50447ef1c92..38dab1f562ed 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -369,6 +369,35 @@ static inline pgd_t pgdp_get(pgd_t *pgdp)
> }
> #endif
>
> +/**
> + * maybe_contiguous_pte_pfns - Hint whether the page mapped by the pte belongs
> + * to a large folio.
> + * @ptep: Pointer to the page table entry.
> + * @pte: The page table entry.
> + *
> + * This helper is invoked when the caller wants to batch over a set of ptes
> + * mapping a large folio, but the concerned code path does not already have
> + * the folio. We want to avoid the cost of vm_normal_folio() only to find that
> + * the underlying folio was small; i.e keep the small folio case as fast as
> + * possible.
> + *
> + * The caller must ensure that ptep + 1 exists.
ptep points to an entry in a PTE page. As long as it is not pointing
to the last entry, ptep+1 should always exist. With PTRS_PER_PTE and
sizeof(pte_t), you can check ptep address to figure out whether it
is the last entry of a PTE page, right? Let me know if I misunderstand
anything.
--
Best Regards,
Yan, Zi
^ permalink raw reply [flat|nested] 23+ messages in thread
* Re: [PATCH v2 2/2] mm: Optimize mremap() by PTE batching
2025-05-08 2:00 ` Zi Yan
@ 2025-05-08 4:01 ` Dev Jain
2025-05-08 6:31 ` Anshuman Khandual
1 sibling, 0 replies; 23+ messages in thread
From: Dev Jain @ 2025-05-08 4:01 UTC (permalink / raw)
To: Zi Yan
Cc: akpm, Liam.Howlett, lorenzo.stoakes, vbabka, jannh, pfalcato,
linux-mm, linux-kernel, david, peterx, ryan.roberts, mingo,
libang.li, maobibo, zhengqi.arch, baohua, anshuman.khandual,
willy, ioworker0, yang, baolin.wang, hughd
On 08/05/25 7:30 am, Zi Yan wrote:
> On 7 May 2025, at 2:02, Dev Jain wrote:
>
>> To use PTE batching, we want to determine whether the folio mapped by
>> the PTE is large, thus requiring the use of vm_normal_folio(). We want
>> to avoid the cost of vm_normal_folio() if the code path doesn't already
>> require the folio. For arm64, pte_batch_hint() does the job. To generalize
>> this hint, add a helper which will determine whether two consecutive PTEs
>> point to consecutive PFNs, in which case there is a high probability that
>> the underlying folio is large.
>> Next, use folio_pte_batch() to optimize move_ptes(). On arm64, if the ptes
>> are painted with the contig bit, then ptep_get() will iterate through all 16
>> entries to collect a/d bits. Hence this optimization will result in a 16x
>> reduction in the number of ptep_get() calls. Next, ptep_get_and_clear()
>> will eventually call contpte_try_unfold() on every contig block, thus
>> flushing the TLB for the complete large folio range. Instead, use
>> get_and_clear_full_ptes() so as to elide TLBIs on each contig block, and only
>> do them on the starting and ending contig block.
>>
>> Signed-off-by: Dev Jain <dev.jain@arm.com>
>> ---
>> include/linux/pgtable.h | 29 +++++++++++++++++++++++++++++
>> mm/mremap.c | 37 ++++++++++++++++++++++++++++++-------
>> 2 files changed, 59 insertions(+), 7 deletions(-)
>>
>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
>> index b50447ef1c92..38dab1f562ed 100644
>> --- a/include/linux/pgtable.h
>> +++ b/include/linux/pgtable.h
>> @@ -369,6 +369,35 @@ static inline pgd_t pgdp_get(pgd_t *pgdp)
>> }
>> #endif
>>
>> +/**
>> + * maybe_contiguous_pte_pfns - Hint whether the page mapped by the pte belongs
>> + * to a large folio.
>> + * @ptep: Pointer to the page table entry.
>> + * @pte: The page table entry.
>> + *
>> + * This helper is invoked when the caller wants to batch over a set of ptes
>> + * mapping a large folio, but the concerned code path does not already have
>> + * the folio. We want to avoid the cost of vm_normal_folio() only to find that
>> + * the underlying folio was small; i.e keep the small folio case as fast as
>> + * possible.
>> + *
>> + * The caller must ensure that ptep + 1 exists.
>
> ptep points to an entry in a PTE page. As long as it is not pointing
> to the last entry, ptep+1 should always exist. With PTRS_PER_PTE and
> sizeof(pte_t), you can check ptep address to figure out whether it
> is the last entry of a PTE page, right? Let me know if I misunderstand
> anything.
Sounds correct to me.
>
>
> --
> Best Regards,
> Yan, Zi
^ permalink raw reply [flat|nested] 23+ messages in thread
* Re: [PATCH v2 2/2] mm: Optimize mremap() by PTE batching
2025-05-08 2:00 ` Zi Yan
2025-05-08 4:01 ` Dev Jain
@ 2025-05-08 6:31 ` Anshuman Khandual
1 sibling, 0 replies; 23+ messages in thread
From: Anshuman Khandual @ 2025-05-08 6:31 UTC (permalink / raw)
To: Zi Yan, Dev Jain
Cc: akpm, Liam.Howlett, lorenzo.stoakes, vbabka, jannh, pfalcato,
linux-mm, linux-kernel, david, peterx, ryan.roberts, mingo,
libang.li, maobibo, zhengqi.arch, baohua, willy, ioworker0, yang,
baolin.wang, hughd
On 5/8/25 07:30, Zi Yan wrote:
> On 7 May 2025, at 2:02, Dev Jain wrote:
>
>> To use PTE batching, we want to determine whether the folio mapped by
>> the PTE is large, thus requiring the use of vm_normal_folio(). We want
>> to avoid the cost of vm_normal_folio() if the code path doesn't already
>> require the folio. For arm64, pte_batch_hint() does the job. To generalize
>> this hint, add a helper which will determine whether two consecutive PTEs
>> point to consecutive PFNs, in which case there is a high probability that
>> the underlying folio is large.
>> Next, use folio_pte_batch() to optimize move_ptes(). On arm64, if the ptes
>> are painted with the contig bit, then ptep_get() will iterate through all 16
>> entries to collect a/d bits. Hence this optimization will result in a 16x
>> reduction in the number of ptep_get() calls. Next, ptep_get_and_clear()
>> will eventually call contpte_try_unfold() on every contig block, thus
>> flushing the TLB for the complete large folio range. Instead, use
>> get_and_clear_full_ptes() so as to elide TLBIs on each contig block, and only
>> do them on the starting and ending contig block.
>>
>> Signed-off-by: Dev Jain <dev.jain@arm.com>
>> ---
>> include/linux/pgtable.h | 29 +++++++++++++++++++++++++++++
>> mm/mremap.c | 37 ++++++++++++++++++++++++++++++-------
>> 2 files changed, 59 insertions(+), 7 deletions(-)
>>
>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
>> index b50447ef1c92..38dab1f562ed 100644
>> --- a/include/linux/pgtable.h
>> +++ b/include/linux/pgtable.h
>> @@ -369,6 +369,35 @@ static inline pgd_t pgdp_get(pgd_t *pgdp)
>> }
>> #endif
>>
>> +/**
>> + * maybe_contiguous_pte_pfns - Hint whether the page mapped by the pte belongs
>> + * to a large folio.
>> + * @ptep: Pointer to the page table entry.
>> + * @pte: The page table entry.
>> + *
>> + * This helper is invoked when the caller wants to batch over a set of ptes
>> + * mapping a large folio, but the concerned code path does not already have
>> + * the folio. We want to avoid the cost of vm_normal_folio() only to find that
>> + * the underlying folio was small; i.e keep the small folio case as fast as
>> + * possible.
>> + *
>> + * The caller must ensure that ptep + 1 exists.
>
> ptep points to an entry in a PTE page. As long as it is not pointing
> to the last entry, ptep+1 should always exist. With PTRS_PER_PTE and
> sizeof(pte_t), you can check ptep address to figure out whether it
> is the last entry of a PTE page, right? Let me know if I misunderstand
> anything.
Agreed, this not-the-last-pte-entry test is definitely required here just
to prevent a potential unmapped access crash. But I do agree with Andrew
that unless there are callers, this should be contained in the call site
itself (mm/mremap.c) with a good explanation.
^ permalink raw reply [flat|nested] 23+ messages in thread
* Re: [PATCH v2 2/2] mm: Optimize mremap() by PTE batching
2025-05-07 6:02 ` [PATCH v2 2/2] mm: Optimize mremap() by PTE batching Dev Jain
2025-05-08 1:37 ` Andrew Morton
2025-05-08 2:00 ` Zi Yan
@ 2025-05-08 7:16 ` Anshuman Khandual
2025-05-08 8:05 ` Dev Jain
2025-05-08 9:40 ` Lorenzo Stoakes
2025-05-08 10:04 ` Lorenzo Stoakes
3 siblings, 2 replies; 23+ messages in thread
From: Anshuman Khandual @ 2025-05-08 7:16 UTC (permalink / raw)
To: Dev Jain, akpm
Cc: Liam.Howlett, lorenzo.stoakes, vbabka, jannh, pfalcato, linux-mm,
linux-kernel, david, peterx, ryan.roberts, mingo, libang.li,
maobibo, zhengqi.arch, baohua, willy, ioworker0, yang,
baolin.wang, ziy, hughd
On 5/7/25 11:32, Dev Jain wrote:
> To use PTE batching, we want to determine whether the folio mapped by
> the PTE is large, thus requiring the use of vm_normal_folio(). We want
> to avoid the cost of vm_normal_folio() if the code path doesn't already
> require the folio. For arm64, pte_batch_hint() does the job. To generalize
> this hint, add a helper which will determine whether two consecutive PTEs
> point to consecutive PFNs, in which case there is a high probability that
> the underlying folio is large.
> Next, use folio_pte_batch() to optimize move_ptes(). On arm64, if the ptes
> are painted with the contig bit, then ptep_get() will iterate through all 16
> entries to collect a/d bits. Hence this optimization will result in a 16x
> reduction in the number of ptep_get() calls. Next, ptep_get_and_clear()
> will eventually call contpte_try_unfold() on every contig block, thus
> flushing the TLB for the complete large folio range. Instead, use
> get_and_clear_full_ptes() so as to elide TLBIs on each contig block, and only
> do them on the starting and ending contig block.
>
> Signed-off-by: Dev Jain <dev.jain@arm.com>
> ---
> include/linux/pgtable.h | 29 +++++++++++++++++++++++++++++
> mm/mremap.c | 37 ++++++++++++++++++++++++++++++-------
> 2 files changed, 59 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index b50447ef1c92..38dab1f562ed 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -369,6 +369,35 @@ static inline pgd_t pgdp_get(pgd_t *pgdp)
> }
> #endif
>
> +/**
> + * maybe_contiguous_pte_pfns - Hint whether the page mapped by the pte belongs
> + * to a large folio.
> + * @ptep: Pointer to the page table entry.
> + * @pte: The page table entry.
> + *
> + * This helper is invoked when the caller wants to batch over a set of ptes
> + * mapping a large folio, but the concerned code path does not already have
> + * the folio. We want to avoid the cost of vm_normal_folio() only to find that
> + * the underlying folio was small; i.e keep the small folio case as fast as
> + * possible.
> + *
> + * The caller must ensure that ptep + 1 exists.
> + */
> +static inline bool maybe_contiguous_pte_pfns(pte_t *ptep, pte_t pte)
> +{
> + pte_t *next_ptep, next_pte;
> +
> + if (pte_batch_hint(ptep, pte) != 1)
> + return true;
> +
> + next_ptep = ptep + 1;
> + next_pte = ptep_get(next_ptep);
> + if (!pte_present(next_pte))
> + return false;
> +
> + return unlikely(pte_pfn(next_pte) - pte_pfn(pte) == 1);
> +}
> +
> #ifndef __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
> static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
> unsigned long address,
> diff --git a/mm/mremap.c b/mm/mremap.c
> index 0163e02e5aa8..9c88a276bec4 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -170,6 +170,23 @@ static pte_t move_soft_dirty_pte(pte_t pte)
> return pte;
> }
>
> +/* mremap a batch of PTEs mapping the same large folio */
> +static int mremap_folio_pte_batch(struct vm_area_struct *vma, unsigned long addr,
> + pte_t *ptep, pte_t pte, int max_nr)
> +{
> + const fpb_t flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
> + struct folio *folio;
> + int nr = 1;
A small nit - s/nr/nr_pages ?
> +
> + if ((max_nr != 1) && maybe_contiguous_pte_pfns(ptep, pte)) {
Like mentioned earlier in v1, could maybe_contiguous_pte_pfns() here
add some additional cost for buffers that are actually not mapped to
contig physical pages.
The test case you have mentioned in the cover demonstrating performance
gains might have always been run just after boot, thus increasing the
probability of contiguous physical mapping, which will not be the case
on fragmented memory systems. In that case the proposed consecutive PFN
comparison will always happen unconditionally without any benefit ?
Just curious.
From V1
--------------------------------------------------------------------
maybe_contiguous_pte_pfns() cost will be applicable for memory
areas greater than a single PAGE_SIZE (i.e max_nr != 1) ? This
helper extracts an additional consecutive pte, ensures that it
is valid mapped and extracts pfn before comparing for the span.
There is some cost associated with the above code sequence which
looks justified for sequential access of memory buffers that has
consecutive physical memory backing. But what happens when such
buffers are less probable, will those buffers take a performance
hit for all the comparisons that just turn out to be negative ?
--------------------------------------------------------------------
> + folio = vm_normal_folio(vma, addr, pte);
> + if (folio && folio_test_large(folio))
> + nr = folio_pte_batch(folio, addr, ptep, pte, max_nr,
> + flags, NULL, NULL, NULL);
> + }
> + return nr;
> +}
> +
> static int move_ptes(struct pagetable_move_control *pmc,
> unsigned long extent, pmd_t *old_pmd, pmd_t *new_pmd)
> {
> @@ -177,7 +194,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
> bool need_clear_uffd_wp = vma_has_uffd_without_event_remap(vma);
> struct mm_struct *mm = vma->vm_mm;
> pte_t *old_ptep, *new_ptep;
> - pte_t pte;
> + pte_t old_pte, pte;
> pmd_t dummy_pmdval;
> spinlock_t *old_ptl, *new_ptl;
> bool force_flush = false;
> @@ -186,6 +203,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
> unsigned long old_end = old_addr + extent;
> unsigned long len = old_end - old_addr;
> int err = 0;
> + int max_nr;
A small nit - s/max_nr/max_nr_pages ?
>
> /*
> * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
> @@ -236,12 +254,13 @@ static int move_ptes(struct pagetable_move_control *pmc,
> flush_tlb_batched_pending(vma->vm_mm);
> arch_enter_lazy_mmu_mode();
>
> - for (; old_addr < old_end; old_ptep++, old_addr += PAGE_SIZE,
> - new_ptep++, new_addr += PAGE_SIZE) {
> - if (pte_none(ptep_get(old_ptep)))
> + for (int nr = 1; old_addr < old_end; old_ptep += nr, old_addr += nr * PAGE_SIZE,
> + new_ptep += nr, new_addr += nr * PAGE_SIZE) {
> + max_nr = (old_end - old_addr) >> PAGE_SHIFT;
> + old_pte = ptep_get(old_ptep);
> + if (pte_none(old_pte))
> continue;
>
> - pte = ptep_get_and_clear(mm, old_addr, old_ptep);
> /*
> * If we are remapping a valid PTE, make sure
> * to flush TLB before we drop the PTL for the
> @@ -253,8 +272,12 @@ static int move_ptes(struct pagetable_move_control *pmc,
> * the TLB entry for the old mapping has been
> * flushed.
> */
> - if (pte_present(pte))
> + if (pte_present(old_pte)) {
> + nr = mremap_folio_pte_batch(vma, old_addr, old_ptep,
> + old_pte, max_nr);
> force_flush = true;
> + }
> + pte = get_and_clear_full_ptes(mm, old_addr, old_ptep, nr, 0);
> pte = move_pte(pte, old_addr, new_addr);
> pte = move_soft_dirty_pte(pte);
>
> @@ -267,7 +290,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
> else if (is_swap_pte(pte))
> pte = pte_swp_clear_uffd_wp(pte);
> }
> - set_pte_at(mm, new_addr, new_ptep, pte);
> + set_ptes(mm, new_addr, new_ptep, pte, nr);
> }
> }
>
^ permalink raw reply [flat|nested] 23+ messages in thread* Re: [PATCH v2 2/2] mm: Optimize mremap() by PTE batching
2025-05-08 7:16 ` Anshuman Khandual
@ 2025-05-08 8:05 ` Dev Jain
2025-05-08 9:40 ` Lorenzo Stoakes
1 sibling, 0 replies; 23+ messages in thread
From: Dev Jain @ 2025-05-08 8:05 UTC (permalink / raw)
To: Anshuman Khandual, akpm
Cc: Liam.Howlett, lorenzo.stoakes, vbabka, jannh, pfalcato, linux-mm,
linux-kernel, david, peterx, ryan.roberts, mingo, libang.li,
maobibo, zhengqi.arch, baohua, willy, ioworker0, yang,
baolin.wang, ziy, hughd
On 08/05/25 12:46 pm, Anshuman Khandual wrote:
> On 5/7/25 11:32, Dev Jain wrote:
>> To use PTE batching, we want to determine whether the folio mapped by
>> the PTE is large, thus requiring the use of vm_normal_folio(). We want
>> to avoid the cost of vm_normal_folio() if the code path doesn't already
>> require the folio. For arm64, pte_batch_hint() does the job. To generalize
>> this hint, add a helper which will determine whether two consecutive PTEs
>> point to consecutive PFNs, in which case there is a high probability that
>> the underlying folio is large.
>> Next, use folio_pte_batch() to optimize move_ptes(). On arm64, if the ptes
>> are painted with the contig bit, then ptep_get() will iterate through all 16
>> entries to collect a/d bits. Hence this optimization will result in a 16x
>> reduction in the number of ptep_get() calls. Next, ptep_get_and_clear()
>> will eventually call contpte_try_unfold() on every contig block, thus
>> flushing the TLB for the complete large folio range. Instead, use
>> get_and_clear_full_ptes() so as to elide TLBIs on each contig block, and only
>> do them on the starting and ending contig block.
>>
>> Signed-off-by: Dev Jain <dev.jain@arm.com>
>> ---
>> include/linux/pgtable.h | 29 +++++++++++++++++++++++++++++
>> mm/mremap.c | 37 ++++++++++++++++++++++++++++++-------
>> 2 files changed, 59 insertions(+), 7 deletions(-)
>>
>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
>> index b50447ef1c92..38dab1f562ed 100644
>> --- a/include/linux/pgtable.h
>> +++ b/include/linux/pgtable.h
>> @@ -369,6 +369,35 @@ static inline pgd_t pgdp_get(pgd_t *pgdp)
>> }
>> #endif
>>
>> +/**
>> + * maybe_contiguous_pte_pfns - Hint whether the page mapped by the pte belongs
>> + * to a large folio.
>> + * @ptep: Pointer to the page table entry.
>> + * @pte: The page table entry.
>> + *
>> + * This helper is invoked when the caller wants to batch over a set of ptes
>> + * mapping a large folio, but the concerned code path does not already have
>> + * the folio. We want to avoid the cost of vm_normal_folio() only to find that
>> + * the underlying folio was small; i.e keep the small folio case as fast as
>> + * possible.
>> + *
>> + * The caller must ensure that ptep + 1 exists.
>> + */
>> +static inline bool maybe_contiguous_pte_pfns(pte_t *ptep, pte_t pte)
>> +{
>> + pte_t *next_ptep, next_pte;
>> +
>> + if (pte_batch_hint(ptep, pte) != 1)
>> + return true;
>> +
>> + next_ptep = ptep + 1;
>> + next_pte = ptep_get(next_ptep);
>> + if (!pte_present(next_pte))
>> + return false;
>> +
>> + return unlikely(pte_pfn(next_pte) - pte_pfn(pte) == 1);
>> +}
>> +
>> #ifndef __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
>> static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
>> unsigned long address,
>> diff --git a/mm/mremap.c b/mm/mremap.c
>> index 0163e02e5aa8..9c88a276bec4 100644
>> --- a/mm/mremap.c
>> +++ b/mm/mremap.c
>> @@ -170,6 +170,23 @@ static pte_t move_soft_dirty_pte(pte_t pte)
>> return pte;
>> }
>>
>> +/* mremap a batch of PTEs mapping the same large folio */
>> +static int mremap_folio_pte_batch(struct vm_area_struct *vma, unsigned long addr,
>> + pte_t *ptep, pte_t pte, int max_nr)
>> +{
>> + const fpb_t flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
>> + struct folio *folio;
>> + int nr = 1;
>
> A small nit - s/nr/nr_pages ?
Well, all other places nr is being used, so I would like to keep it
simple and stick to convention :)
>
>> +
>> + if ((max_nr != 1) && maybe_contiguous_pte_pfns(ptep, pte)) {
>
> Like mentioned earlier in v1, could maybe_contiguous_pte_pfns() here
> add some additional cost for buffers that are actually not mapped to
> contig physical pages.
>
> The test case you have mentioned in the cover demonstrating performance
> gains might have always been run just after boot, thus increasing the
> probability of contiguous physical mapping, which will not be the case
> on fragmented memory systems. In that case the proposed consecutive PFN
> comparison will always happen unconditionally without any benefit ?
I think you mean to say that the underlying folio may not be actually
large but the buddy allocator distributed consecutive physical memory.
Hmm...at this rate I am thinking that the overhead of vm_normal_folio()
+ folio_test_large() is acceptable and is less churn :) Would like to
hear your thoughts.
>
> Just curious.
>
> From V1
>
> --------------------------------------------------------------------
> maybe_contiguous_pte_pfns() cost will be applicable for memory
> areas greater than a single PAGE_SIZE (i.e max_nr != 1) ? This
> helper extracts an additional consecutive pte, ensures that it
> is valid mapped and extracts pfn before comparing for the span.
>
> There is some cost associated with the above code sequence which
> looks justified for sequential access of memory buffers that has
> consecutive physical memory backing. But what happens when such
> buffers are less probable, will those buffers take a performance
> hit for all the comparisons that just turn out to be negative ?
> --------------------------------------------------------------------
>
>> + folio = vm_normal_folio(vma, addr, pte);
>> + if (folio && folio_test_large(folio))
>> + nr = folio_pte_batch(folio, addr, ptep, pte, max_nr,
>> + flags, NULL, NULL, NULL);
>> + }
>> + return nr;
>> +}
>> +
>> static int move_ptes(struct pagetable_move_control *pmc,
>> unsigned long extent, pmd_t *old_pmd, pmd_t *new_pmd)
>> {
>> @@ -177,7 +194,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
>> bool need_clear_uffd_wp = vma_has_uffd_without_event_remap(vma);
>> struct mm_struct *mm = vma->vm_mm;
>> pte_t *old_ptep, *new_ptep;
>> - pte_t pte;
>> + pte_t old_pte, pte;
>> pmd_t dummy_pmdval;
>> spinlock_t *old_ptl, *new_ptl;
>> bool force_flush = false;
>> @@ -186,6 +203,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
>> unsigned long old_end = old_addr + extent;
>> unsigned long len = old_end - old_addr;
>> int err = 0;
>> + int max_nr;
>
> A small nit - s/max_nr/max_nr_pages ?
>
>>
>> /*
>> * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
>> @@ -236,12 +254,13 @@ static int move_ptes(struct pagetable_move_control *pmc,
>> flush_tlb_batched_pending(vma->vm_mm);
>> arch_enter_lazy_mmu_mode();
>>
>> - for (; old_addr < old_end; old_ptep++, old_addr += PAGE_SIZE,
>> - new_ptep++, new_addr += PAGE_SIZE) {
>> - if (pte_none(ptep_get(old_ptep)))
>> + for (int nr = 1; old_addr < old_end; old_ptep += nr, old_addr += nr * PAGE_SIZE,
>> + new_ptep += nr, new_addr += nr * PAGE_SIZE) {
>
>
>> + max_nr = (old_end - old_addr) >> PAGE_SHIFT;
>> + old_pte = ptep_get(old_ptep);
>> + if (pte_none(old_pte))
>> continue;
>>
>> - pte = ptep_get_and_clear(mm, old_addr, old_ptep);
>> /*
>> * If we are remapping a valid PTE, make sure
>> * to flush TLB before we drop the PTL for the
>> @@ -253,8 +272,12 @@ static int move_ptes(struct pagetable_move_control *pmc,
>> * the TLB entry for the old mapping has been
>> * flushed.
>> */
>> - if (pte_present(pte))
>> + if (pte_present(old_pte)) {
>> + nr = mremap_folio_pte_batch(vma, old_addr, old_ptep,
>> + old_pte, max_nr);
>> force_flush = true;
>> + }
>> + pte = get_and_clear_full_ptes(mm, old_addr, old_ptep, nr, 0);
>> pte = move_pte(pte, old_addr, new_addr);
>> pte = move_soft_dirty_pte(pte);
>>
>> @@ -267,7 +290,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
>> else if (is_swap_pte(pte))
>> pte = pte_swp_clear_uffd_wp(pte);
>> }
>> - set_pte_at(mm, new_addr, new_ptep, pte);
>> + set_ptes(mm, new_addr, new_ptep, pte, nr);
>> }
>> }
>>
^ permalink raw reply [flat|nested] 23+ messages in thread* Re: [PATCH v2 2/2] mm: Optimize mremap() by PTE batching
2025-05-08 7:16 ` Anshuman Khandual
2025-05-08 8:05 ` Dev Jain
@ 2025-05-08 9:40 ` Lorenzo Stoakes
1 sibling, 0 replies; 23+ messages in thread
From: Lorenzo Stoakes @ 2025-05-08 9:40 UTC (permalink / raw)
To: Anshuman Khandual
Cc: Dev Jain, akpm, Liam.Howlett, vbabka, jannh, pfalcato, linux-mm,
linux-kernel, david, peterx, ryan.roberts, mingo, libang.li,
maobibo, zhengqi.arch, baohua, willy, ioworker0, yang,
baolin.wang, ziy, hughd
On Thu, May 08, 2025 at 12:46:41PM +0530, Anshuman Khandual wrote:
> On 5/7/25 11:32, Dev Jain wrote:
[snip]
> > +/* mremap a batch of PTEs mapping the same large folio */
> > +static int mremap_folio_pte_batch(struct vm_area_struct *vma, unsigned long addr,
> > + pte_t *ptep, pte_t pte, int max_nr)
> > +{
> > + const fpb_t flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
> > + struct folio *folio;
> > + int nr = 1;
>
> A small nit - s/nr/nr_pages ?
Agree in principal, but I think nr_ptes is clearer. You might not even be
dealing with a page, if you hit a pte_none() pte for instance.
So max_nr_ptes, nr_ptes.
^ permalink raw reply [flat|nested] 23+ messages in thread
* Re: [PATCH v2 2/2] mm: Optimize mremap() by PTE batching
2025-05-07 6:02 ` [PATCH v2 2/2] mm: Optimize mremap() by PTE batching Dev Jain
` (2 preceding siblings ...)
2025-05-08 7:16 ` Anshuman Khandual
@ 2025-05-08 10:04 ` Lorenzo Stoakes
2025-05-08 18:01 ` David Hildenbrand
2025-05-18 8:17 ` Dev Jain
3 siblings, 2 replies; 23+ messages in thread
From: Lorenzo Stoakes @ 2025-05-08 10:04 UTC (permalink / raw)
To: Dev Jain
Cc: akpm, Liam.Howlett, vbabka, jannh, pfalcato, linux-mm,
linux-kernel, david, peterx, ryan.roberts, mingo, libang.li,
maobibo, zhengqi.arch, baohua, anshuman.khandual, willy,
ioworker0, yang, baolin.wang, ziy, hughd
Before getting into the review, just to say thanks for refactoring as per
my (and of course other's) comments, much appreciated and big improvement!
:)
We're getting there...
On Wed, May 07, 2025 at 11:32:56AM +0530, Dev Jain wrote:
> To use PTE batching, we want to determine whether the folio mapped by
> the PTE is large, thus requiring the use of vm_normal_folio(). We want
> to avoid the cost of vm_normal_folio() if the code path doesn't already
> require the folio. For arm64, pte_batch_hint() does the job. To generalize
> this hint, add a helper which will determine whether two consecutive PTEs
> point to consecutive PFNs, in which case there is a high probability that
> the underlying folio is large.
> Next, use folio_pte_batch() to optimize move_ptes(). On arm64, if the ptes
> are painted with the contig bit, then ptep_get() will iterate through all 16
> entries to collect a/d bits. Hence this optimization will result in a 16x
> reduction in the number of ptep_get() calls. Next, ptep_get_and_clear()
> will eventually call contpte_try_unfold() on every contig block, thus
> flushing the TLB for the complete large folio range. Instead, use
> get_and_clear_full_ptes() so as to elide TLBIs on each contig block, and only
> do them on the starting and ending contig block.
>
> Signed-off-by: Dev Jain <dev.jain@arm.com>
> ---
> include/linux/pgtable.h | 29 +++++++++++++++++++++++++++++
> mm/mremap.c | 37 ++++++++++++++++++++++++++++++-------
> 2 files changed, 59 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index b50447ef1c92..38dab1f562ed 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -369,6 +369,35 @@ static inline pgd_t pgdp_get(pgd_t *pgdp)
> }
> #endif
>
> +/**
> + * maybe_contiguous_pte_pfns - Hint whether the page mapped by the pte belongs
> + * to a large folio.
> + * @ptep: Pointer to the page table entry.
> + * @pte: The page table entry.
> + *
> + * This helper is invoked when the caller wants to batch over a set of ptes
> + * mapping a large folio, but the concerned code path does not already have
> + * the folio. We want to avoid the cost of vm_normal_folio() only to find that
> + * the underlying folio was small; i.e keep the small folio case as fast as
> + * possible.
> + *
> + * The caller must ensure that ptep + 1 exists.
> + */
> +static inline bool maybe_contiguous_pte_pfns(pte_t *ptep, pte_t pte)
> +{
> + pte_t *next_ptep, next_pte;
> +
> + if (pte_batch_hint(ptep, pte) != 1)
> + return true;
> +
> + next_ptep = ptep + 1;
> + next_pte = ptep_get(next_ptep);
> + if (!pte_present(next_pte))
> + return false;
> +
> + return unlikely(pte_pfn(next_pte) - pte_pfn(pte) == 1);
Let's not do unlikely()'s unless we have data for them... it shouldn't mean
'what the programmer believes' :)
> +}
Yeah I'm with Andrew and Anshuman, I mean this is kind of a nasty interface
(I mean _perhaps_ unavoidably) and we've done the relevant check in
mremap_folio_pte_batch(), so let's just move it there with comments, as this
> +
> #ifndef __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
> static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
> unsigned long address,
> diff --git a/mm/mremap.c b/mm/mremap.c
> index 0163e02e5aa8..9c88a276bec4 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -170,6 +170,23 @@ static pte_t move_soft_dirty_pte(pte_t pte)
> return pte;
> }
>
> +/* mremap a batch of PTEs mapping the same large folio */
> +static int mremap_folio_pte_batch(struct vm_area_struct *vma, unsigned long addr,
> + pte_t *ptep, pte_t pte, int max_nr)
> +{
> + const fpb_t flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
> + struct folio *folio;
> + int nr = 1;
> +
> + if ((max_nr != 1) && maybe_contiguous_pte_pfns(ptep, pte)) {
> + folio = vm_normal_folio(vma, addr, pte);
> + if (folio && folio_test_large(folio))
> + nr = folio_pte_batch(folio, addr, ptep, pte, max_nr,
> + flags, NULL, NULL, NULL);
> + }
This needs some refactoring, avoid nesting at all costs :)
We'll want to move the maybe_contiguous_pte_pfns() function over here, so
that'll change things, but in general let's use a guard clause.
So an if block like:
if (foo) {
... bunch of logic ...
}
Is better replaced with a guard clause so you have:
if (!foo)
return ...;
... bunch of logic ...
Here we could really expand things out to make things SUPER clear like:
static int mremap_folio_pte_batch(struct vm_area_struct *vma, unsigned long addr,
pte_t *ptep, pte_t pte, int max_nr)
{
const fpb_t flags;
struct folio *folio;
if (max_nr == 1)
return 1;
if (!maybe_contiguous_pte_pfns(ptep, pte)) // obviously replace with open code...
return 1;
folio = vm_normal_folio(vma, addr, pte);
if (!folio)
return 1;
if (!folio_test_large(folio))
return 1;
flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
return folio_pte_batch(folio, addr, ptep, pte, max_nr,
flags, NULL, NULL, NULL);
}
I mean you could argue assign nr would be neater here, but you get the point!
David mentioned a point about this code over in v1 discussion (see
[0]). Trying to bring converastion here to avoid it being split across
old/new series. There he said:
David H:
> (2) Do we really need "must be part of the same folio", or could be just batch over present
> ptes that map consecutive PFNs? In that case, a helper that avoids folio_pte_batch() completely
> might be better.
Hm, if we didn't do the batch test, can we batch a split large folio here ok?
I'm guessing we can in which case this check is actually limiting...
Are we _explicitly_ only considering the cont pte case and ignoring the
split THP case?
[0]: https://lore.kernel.org/all/887fb371-409e-4dad-b4ff-38b85bfddf95@redhat.com/
And in what circumstances will the hint be set, with a present subsequent
PTE but !folio_test_large()?
I guess the hint might not be taken? But then isn't the valid check just
folio_test_large() and we don't need this batched check at all?
Is it only to avoid the split THP case?
We definitely need some clarity here, and a comment in the code explaining
what's going on as this is subtle stuff.
> + return nr;
> +}
> +
> static int move_ptes(struct pagetable_move_control *pmc,
> unsigned long extent, pmd_t *old_pmd, pmd_t *new_pmd)
> {
> @@ -177,7 +194,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
> bool need_clear_uffd_wp = vma_has_uffd_without_event_remap(vma);
> struct mm_struct *mm = vma->vm_mm;
> pte_t *old_ptep, *new_ptep;
> - pte_t pte;
> + pte_t old_pte, pte;
> pmd_t dummy_pmdval;
> spinlock_t *old_ptl, *new_ptl;
> bool force_flush = false;
> @@ -186,6 +203,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
> unsigned long old_end = old_addr + extent;
> unsigned long len = old_end - old_addr;
> int err = 0;
> + int max_nr;
>
> /*
> * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
> @@ -236,12 +254,13 @@ static int move_ptes(struct pagetable_move_control *pmc,
> flush_tlb_batched_pending(vma->vm_mm);
> arch_enter_lazy_mmu_mode();
>
> - for (; old_addr < old_end; old_ptep++, old_addr += PAGE_SIZE,
> - new_ptep++, new_addr += PAGE_SIZE) {
> - if (pte_none(ptep_get(old_ptep)))
> + for (int nr = 1; old_addr < old_end; old_ptep += nr, old_addr += nr * PAGE_SIZE,
> + new_ptep += nr, new_addr += nr * PAGE_SIZE) {
Really nitty thing here but the indentation is all messed up here, I mean
nothing is going to be nice but maybe indent by two tabs below 'for'.
I'm not a fan of this declaration of nr, typically in a for loop a declaration
here would be the counter, so this is just confusing.
In the old implementation, declaring nr in the for loop would make sense,
but in the newly refactored one you should just declare it at the top.
Also as per Anshuman review, I think nr_ptes, max_nr_ptes would be better.
I don't think 'nr' needs to be initialised either, since the conditional is
'old_addr < old_end' and you _should_ only perform the
> + max_nr = (old_end - old_addr) >> PAGE_SHIFT;
> + old_pte = ptep_get(old_ptep);
> + if (pte_none(old_pte))
This seems broken.
You're missing a nr assignment here, so you'll happen to offset by the
number of pages of the last folio you encountered?
Should be:
if (pte_none(old_pte)) {
nr_ptes = 1;
continue;
}
Or, alternatively, you can reset nr_ptes to 1 at the start of each loop.
> continue;
>
> - pte = ptep_get_and_clear(mm, old_addr, old_ptep);
> /*
> * If we are remapping a valid PTE, make sure
> * to flush TLB before we drop the PTL for the
> @@ -253,8 +272,12 @@ static int move_ptes(struct pagetable_move_control *pmc,
> * the TLB entry for the old mapping has been
> * flushed.
> */
> - if (pte_present(pte))
> + if (pte_present(old_pte)) {
> + nr = mremap_folio_pte_batch(vma, old_addr, old_ptep,
> + old_pte, max_nr);
> force_flush = true;
> + }
Thanks this is much clearer compared to v1
> + pte = get_and_clear_full_ptes(mm, old_addr, old_ptep, nr, 0);
Nit but...
Can we have a comment indicating what the last parameter refers to? I think
David maybe doens't like this so obviously if he prefers not that fine, but
I'm thinking something like:
pte = get_and_clear_full_ptes(mm, old_addr, old_ptep, nr, /*full=*/false);
I think we are good to just use 'false' here right? As it's only an int for
historical purposes...
> pte = move_pte(pte, old_addr, new_addr);
> pte = move_soft_dirty_pte(pte);
>
> @@ -267,7 +290,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
> else if (is_swap_pte(pte))
> pte = pte_swp_clear_uffd_wp(pte);
> }
> - set_pte_at(mm, new_addr, new_ptep, pte);
> + set_ptes(mm, new_addr, new_ptep, pte, nr);
> }
> }
>
> --
> 2.30.2
>
^ permalink raw reply [flat|nested] 23+ messages in thread* Re: [PATCH v2 2/2] mm: Optimize mremap() by PTE batching
2025-05-08 10:04 ` Lorenzo Stoakes
@ 2025-05-08 18:01 ` David Hildenbrand
2025-05-18 8:17 ` Dev Jain
1 sibling, 0 replies; 23+ messages in thread
From: David Hildenbrand @ 2025-05-08 18:01 UTC (permalink / raw)
To: Lorenzo Stoakes, Dev Jain
Cc: akpm, Liam.Howlett, vbabka, jannh, pfalcato, linux-mm,
linux-kernel, peterx, ryan.roberts, mingo, libang.li, maobibo,
zhengqi.arch, baohua, anshuman.khandual, willy, ioworker0, yang,
baolin.wang, ziy, hughd
On 08.05.25 12:04, Lorenzo Stoakes wrote:
> Before getting into the review, just to say thanks for refactoring as per
> my (and of course other's) comments, much appreciated and big improvement!
> :)
>
> We're getting there...
>
> On Wed, May 07, 2025 at 11:32:56AM +0530, Dev Jain wrote:
>> To use PTE batching, we want to determine whether the folio mapped by
>> the PTE is large, thus requiring the use of vm_normal_folio(). We want
>> to avoid the cost of vm_normal_folio() if the code path doesn't already
>> require the folio. For arm64, pte_batch_hint() does the job. To generalize
>> this hint, add a helper which will determine whether two consecutive PTEs
>> point to consecutive PFNs, in which case there is a high probability that
>> the underlying folio is large.
>> Next, use folio_pte_batch() to optimize move_ptes(). On arm64, if the ptes
>> are painted with the contig bit, then ptep_get() will iterate through all 16
>> entries to collect a/d bits. Hence this optimization will result in a 16x
>> reduction in the number of ptep_get() calls. Next, ptep_get_and_clear()
>> will eventually call contpte_try_unfold() on every contig block, thus
>> flushing the TLB for the complete large folio range. Instead, use
>> get_and_clear_full_ptes() so as to elide TLBIs on each contig block, and only
>> do them on the starting and ending contig block.
>>
>> Signed-off-by: Dev Jain <dev.jain@arm.com>
>> ---
>> include/linux/pgtable.h | 29 +++++++++++++++++++++++++++++
>> mm/mremap.c | 37 ++++++++++++++++++++++++++++++-------
>> 2 files changed, 59 insertions(+), 7 deletions(-)
>>
>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
>> index b50447ef1c92..38dab1f562ed 100644
>> --- a/include/linux/pgtable.h
>> +++ b/include/linux/pgtable.h
>> @@ -369,6 +369,35 @@ static inline pgd_t pgdp_get(pgd_t *pgdp)
>> }
>> #endif
>>
>> +/**
>> + * maybe_contiguous_pte_pfns - Hint whether the page mapped by the pte belongs
>> + * to a large folio.
>> + * @ptep: Pointer to the page table entry.
>> + * @pte: The page table entry.
>> + *
>> + * This helper is invoked when the caller wants to batch over a set of ptes
>> + * mapping a large folio, but the concerned code path does not already have
>> + * the folio. We want to avoid the cost of vm_normal_folio() only to find that
>> + * the underlying folio was small; i.e keep the small folio case as fast as
>> + * possible.
>> + *
>> + * The caller must ensure that ptep + 1 exists.
>> + */
>> +static inline bool maybe_contiguous_pte_pfns(pte_t *ptep, pte_t pte)
>> +{
>> + pte_t *next_ptep, next_pte;
>> +
>> + if (pte_batch_hint(ptep, pte) != 1)
>> + return true;
>> +
>> + next_ptep = ptep + 1;
>> + next_pte = ptep_get(next_ptep);
>> + if (!pte_present(next_pte))
>> + return false;
>> +
>> + return unlikely(pte_pfn(next_pte) - pte_pfn(pte) == 1);
>
> Let's not do unlikely()'s unless we have data for them... it shouldn't mean
> 'what the programmer believes' :)
>
>> +}
>
> Yeah I'm with Andrew and Anshuman, I mean this is kind of a nasty interface
> (I mean _perhaps_ unavoidably) and we've done the relevant check in
> mremap_folio_pte_batch(), so let's just move it there with comments, as this
>
>> +
>> #ifndef __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
>> static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
>> unsigned long address,
>> diff --git a/mm/mremap.c b/mm/mremap.c
>> index 0163e02e5aa8..9c88a276bec4 100644
>> --- a/mm/mremap.c
>> +++ b/mm/mremap.c
>> @@ -170,6 +170,23 @@ static pte_t move_soft_dirty_pte(pte_t pte)
>> return pte;
>> }
>>
>> +/* mremap a batch of PTEs mapping the same large folio */
>> +static int mremap_folio_pte_batch(struct vm_area_struct *vma, unsigned long addr,
>> + pte_t *ptep, pte_t pte, int max_nr)
>> +{
>> + const fpb_t flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
>> + struct folio *folio;
>> + int nr = 1;
>> +
>> + if ((max_nr != 1) && maybe_contiguous_pte_pfns(ptep, pte)) {
>> + folio = vm_normal_folio(vma, addr, pte);
>> + if (folio && folio_test_large(folio))
>> + nr = folio_pte_batch(folio, addr, ptep, pte, max_nr,
>> + flags, NULL, NULL, NULL);
>> + }
>
> This needs some refactoring, avoid nesting at all costs :)
>
> We'll want to move the maybe_contiguous_pte_pfns() function over here, so
> that'll change things, but in general let's use a guard clause.
>
> So an if block like:
>
> if (foo) {
> ... bunch of logic ...
> }
>
> Is better replaced with a guard clause so you have:
>
> if (!foo)
> return ...;
>
> ... bunch of logic ...
>
> Here we could really expand things out to make things SUPER clear like:
>
> static int mremap_folio_pte_batch(struct vm_area_struct *vma, unsigned long addr,
> pte_t *ptep, pte_t pte, int max_nr)
> {
> const fpb_t flags;
> struct folio *folio;
>
> if (max_nr == 1)
> return 1;
> if (!maybe_contiguous_pte_pfns(ptep, pte)) // obviously replace with open code...
> return 1;
>
> folio = vm_normal_folio(vma, addr, pte);
> if (!folio)
> return 1;
> if (!folio_test_large(folio))
> return 1;
>
> flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
> return folio_pte_batch(folio, addr, ptep, pte, max_nr,
> flags, NULL, NULL, NULL);
> }
>
> I mean you could argue assign nr would be neater here, but you get the point!
>
> David mentioned a point about this code over in v1 discussion (see
> [0]). Trying to bring converastion here to avoid it being split across
> old/new series. There he said:
>
> David H:
>> (2) Do we really need "must be part of the same folio", or could be just batch over present
>> ptes that map consecutive PFNs? In that case, a helper that avoids folio_pte_batch() completely
>> might be better.
>
> Hm, if we didn't do the batch test, can we batch a split large folio here ok?
> I'm guessing we can in which case this check is actually limiting...
>
> Are we _explicitly_ only considering the cont pte case and ignoring the
> split THP case?
>
> [0]: https://lore.kernel.org/all/887fb371-409e-4dad-b4ff-38b85bfddf95@redhat.com/
>
> And in what circumstances will the hint be set, with a present subsequent
> PTE but !folio_test_large()?
>
> I guess the hint might not be taken? But then isn't the valid check just
> folio_test_large() and we don't need this batched check at all?
>
> Is it only to avoid the split THP case?
>
> We definitely need some clarity here, and a comment in the code explaining
> what's going on as this is subtle stuff.
The whole maybe_contiguous_pte_pfns() is really far from nice. Let's add
something like that *only if absolutely required* for performance
reasons and on top of this patch.
But let's clarify if we have to limit ourselves to a single folio at all.
Staring at it, I think the tricky bit is:
pte = get_and_clear_full_ptes();
That means that
a) if any PTE is dirty, the resulting PTE will be dirty.
b) if any PTE is young, the resulting PTE will be young.
So we could be marking PTEs as dirty/young from unrelated folios.
That's problematic.
--
Cheers,
David / dhildenb
^ permalink raw reply [flat|nested] 23+ messages in thread* Re: [PATCH v2 2/2] mm: Optimize mremap() by PTE batching
2025-05-08 10:04 ` Lorenzo Stoakes
2025-05-08 18:01 ` David Hildenbrand
@ 2025-05-18 8:17 ` Dev Jain
2025-05-19 9:04 ` Lorenzo Stoakes
1 sibling, 1 reply; 23+ messages in thread
From: Dev Jain @ 2025-05-18 8:17 UTC (permalink / raw)
To: Lorenzo Stoakes
Cc: akpm, Liam.Howlett, vbabka, jannh, pfalcato, linux-mm,
linux-kernel, david, peterx, ryan.roberts, mingo, libang.li,
maobibo, zhengqi.arch, baohua, anshuman.khandual, willy,
ioworker0, yang, baolin.wang, ziy, hughd
On 08/05/25 3:34 pm, Lorenzo Stoakes wrote:
> Before getting into the review, just to say thanks for refactoring as per
> my (and of course other's) comments, much appreciated and big improvement!
> :)
>
> We're getting there...
>
> On Wed, May 07, 2025 at 11:32:56AM +0530, Dev Jain wrote:
>> To use PTE batching, we want to determine whether the folio mapped by
>> the PTE is large, thus requiring the use of vm_normal_folio(). We want
>> to avoid the cost of vm_normal_folio() if the code path doesn't already
>> require the folio. For arm64, pte_batch_hint() does the job. To generalize
>> this hint, add a helper which will determine whether two consecutive PTEs
>> point to consecutive PFNs, in which case there is a high probability that
>> the underlying folio is large.
>> Next, use folio_pte_batch() to optimize move_ptes(). On arm64, if the ptes
>> are painted with the contig bit, then ptep_get() will iterate through all 16
>> entries to collect a/d bits. Hence this optimization will result in a 16x
>> reduction in the number of ptep_get() calls. Next, ptep_get_and_clear()
>> will eventually call contpte_try_unfold() on every contig block, thus
>> flushing the TLB for the complete large folio range. Instead, use
>> get_and_clear_full_ptes() so as to elide TLBIs on each contig block, and only
>> do them on the starting and ending contig block.
>>
>> Signed-off-by: Dev Jain <dev.jain@arm.com>
>> ---
>> include/linux/pgtable.h | 29 +++++++++++++++++++++++++++++
>> mm/mremap.c | 37 ++++++++++++++++++++++++++++++-------
>> 2 files changed, 59 insertions(+), 7 deletions(-)
>>
>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
>> index b50447ef1c92..38dab1f562ed 100644
>> --- a/include/linux/pgtable.h
>> +++ b/include/linux/pgtable.h
>> @@ -369,6 +369,35 @@ static inline pgd_t pgdp_get(pgd_t *pgdp)
>> }
>> #endif
>>
>> +/**
>> + * maybe_contiguous_pte_pfns - Hint whether the page mapped by the pte belongs
>> + * to a large folio.
>> + * @ptep: Pointer to the page table entry.
>> + * @pte: The page table entry.
>> + *
>> + * This helper is invoked when the caller wants to batch over a set of ptes
>> + * mapping a large folio, but the concerned code path does not already have
>> + * the folio. We want to avoid the cost of vm_normal_folio() only to find that
>> + * the underlying folio was small; i.e keep the small folio case as fast as
>> + * possible.
>> + *
>> + * The caller must ensure that ptep + 1 exists.
>> + */
>> +static inline bool maybe_contiguous_pte_pfns(pte_t *ptep, pte_t pte)
>> +{
>> + pte_t *next_ptep, next_pte;
>> +
>> + if (pte_batch_hint(ptep, pte) != 1)
>> + return true;
>> +
>> + next_ptep = ptep + 1;
>> + next_pte = ptep_get(next_ptep);
>> + if (!pte_present(next_pte))
>> + return false;
>> +
>> + return unlikely(pte_pfn(next_pte) - pte_pfn(pte) == 1);
>
> Let's not do unlikely()'s unless we have data for them... it shouldn't mean
> 'what the programmer believes' :)
>
>> +}
>
> Yeah I'm with Andrew and Anshuman, I mean this is kind of a nasty interface
> (I mean _perhaps_ unavoidably) and we've done the relevant check in
> mremap_folio_pte_batch(), so let's just move it there with comments, as this
>
>> +
>> #ifndef __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
>> static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
>> unsigned long address,
>> diff --git a/mm/mremap.c b/mm/mremap.c
>> index 0163e02e5aa8..9c88a276bec4 100644
>> --- a/mm/mremap.c
>> +++ b/mm/mremap.c
>> @@ -170,6 +170,23 @@ static pte_t move_soft_dirty_pte(pte_t pte)
>> return pte;
>> }
>>
>> +/* mremap a batch of PTEs mapping the same large folio */
>> +static int mremap_folio_pte_batch(struct vm_area_struct *vma, unsigned long addr,
>> + pte_t *ptep, pte_t pte, int max_nr)
>> +{
>> + const fpb_t flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
>> + struct folio *folio;
>> + int nr = 1;
>> +
>> + if ((max_nr != 1) && maybe_contiguous_pte_pfns(ptep, pte)) {
>> + folio = vm_normal_folio(vma, addr, pte);
>> + if (folio && folio_test_large(folio))
>> + nr = folio_pte_batch(folio, addr, ptep, pte, max_nr,
>> + flags, NULL, NULL, NULL);
>> + }
>
> This needs some refactoring, avoid nesting at all costs :)
>
> We'll want to move the maybe_contiguous_pte_pfns() function over here, so
> that'll change things, but in general let's use a guard clause.
>
> So an if block like:
>
> if (foo) {
> ... bunch of logic ...
> }
>
> Is better replaced with a guard clause so you have:
>
> if (!foo)
> return ...;
>
> ... bunch of logic ...
>
> Here we could really expand things out to make things SUPER clear like:
>
> static int mremap_folio_pte_batch(struct vm_area_struct *vma, unsigned long addr,
> pte_t *ptep, pte_t pte, int max_nr)
> {
> const fpb_t flags;
> struct folio *folio;
>
> if (max_nr == 1)
> return 1;
> if (!maybe_contiguous_pte_pfns(ptep, pte)) // obviously replace with open code...
> return 1;
>
> folio = vm_normal_folio(vma, addr, pte);
> if (!folio)
> return 1;
> if (!folio_test_large(folio))
> return 1;
>
> flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
> return folio_pte_batch(folio, addr, ptep, pte, max_nr,
> flags, NULL, NULL, NULL);
> }
>
> I mean you could argue assign nr would be neater here, but you get the point!
>
> David mentioned a point about this code over in v1 discussion (see
> [0]). Trying to bring converastion here to avoid it being split across
> old/new series. There he said:
>
> David H:
>> (2) Do we really need "must be part of the same folio", or could be just batch over present
>> ptes that map consecutive PFNs? In that case, a helper that avoids folio_pte_batch() completely
>> might be better.
>
> Hm, if we didn't do the batch test, can we batch a split large folio here ok?
> I'm guessing we can in which case this check is actually limiting...
>
> Are we _explicitly_ only considering the cont pte case and ignoring the
> split THP case?
>
> [0]: https://lore.kernel.org/all/887fb371-409e-4dad-b4ff-38b85bfddf95@redhat.com/
>
> And in what circumstances will the hint be set, with a present subsequent
> PTE but !folio_test_large()?
>
> I guess the hint might not be taken? But then isn't the valid check just
> folio_test_large() and we don't need this batched check at all?
>
> Is it only to avoid the split THP case?
>
> We definitely need some clarity here, and a comment in the code explaining
> what's going on as this is subtle stuff.
I am focussed only on batching large folios. Split THPs won't be
batched; you can use pte_batch() (from David's refactoring) and
figure the split THP batch out, but then get_and_clear_full_ptes()
will be gathering a/d bits and smearing them across the batch, which
will be incorrect. Even if we introduce a new version of
get_and_clear_full_ptes() which does not gather a/d bits, then if the
pte_batch actually belongs to a folio, then we will *not* be smearing
a/d bits, which is again wrong. So in any case we must know what the
underlying folio looks like :) So my agenda for v3 is,
- Incorporate your refactoring comments
- Remove maybe_contiguous_pte_pfns and just use vm_normal_folio +
folio_test_large
- Fix indentation
Sounds good?
>
>> + return nr;
>> +}
>> +
>> static int move_ptes(struct pagetable_move_control *pmc,
>> unsigned long extent, pmd_t *old_pmd, pmd_t *new_pmd)
>> {
>> @@ -177,7 +194,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
>> bool need_clear_uffd_wp = vma_has_uffd_without_event_remap(vma);
>> struct mm_struct *mm = vma->vm_mm;
>> pte_t *old_ptep, *new_ptep;
>> - pte_t pte;
>> + pte_t old_pte, pte;
>> pmd_t dummy_pmdval;
>> spinlock_t *old_ptl, *new_ptl;
>> bool force_flush = false;
>> @@ -186,6 +203,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
>> unsigned long old_end = old_addr + extent;
>> unsigned long len = old_end - old_addr;
>> int err = 0;
>> + int max_nr;
>>
>> /*
>> * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
>> @@ -236,12 +254,13 @@ static int move_ptes(struct pagetable_move_control *pmc,
>> flush_tlb_batched_pending(vma->vm_mm);
>> arch_enter_lazy_mmu_mode();
>>
>> - for (; old_addr < old_end; old_ptep++, old_addr += PAGE_SIZE,
>> - new_ptep++, new_addr += PAGE_SIZE) {
>> - if (pte_none(ptep_get(old_ptep)))
>> + for (int nr = 1; old_addr < old_end; old_ptep += nr, old_addr += nr * PAGE_SIZE,
>> + new_ptep += nr, new_addr += nr * PAGE_SIZE) {
>
> Really nitty thing here but the indentation is all messed up here, I mean
> nothing is going to be nice but maybe indent by two tabs below 'for'.
>
> I'm not a fan of this declaration of nr, typically in a for loop a declaration
> here would be the counter, so this is just confusing.
>
> In the old implementation, declaring nr in the for loop would make sense,
> but in the newly refactored one you should just declare it at the top.
>
> Also as per Anshuman review, I think nr_ptes, max_nr_ptes would be better.
>
> I don't think 'nr' needs to be initialised either, since the conditional is
> 'old_addr < old_end' and you _should_ only perform the
>
>> + max_nr = (old_end - old_addr) >> PAGE_SHIFT;
>> + old_pte = ptep_get(old_ptep);
>> + if (pte_none(old_pte))
>
> This seems broken.
>
> You're missing a nr assignment here, so you'll happen to offset by the
> number of pages of the last folio you encountered?
>
> Should be:
>
> if (pte_none(old_pte)) {
> nr_ptes = 1;
> continue;
> }
>
> Or, alternatively, you can reset nr_ptes to 1 at the start of each loop.
>
>
>> continue;
>>
>> - pte = ptep_get_and_clear(mm, old_addr, old_ptep);
>
>> /*
>> * If we are remapping a valid PTE, make sure
>> * to flush TLB before we drop the PTL for the
>> @@ -253,8 +272,12 @@ static int move_ptes(struct pagetable_move_control *pmc,
>> * the TLB entry for the old mapping has been
>> * flushed.
>> */
>> - if (pte_present(pte))
>> + if (pte_present(old_pte)) {
>> + nr = mremap_folio_pte_batch(vma, old_addr, old_ptep,
>> + old_pte, max_nr);
>> force_flush = true;
>> + }
>
> Thanks this is much clearer compared to v1
>
>> + pte = get_and_clear_full_ptes(mm, old_addr, old_ptep, nr, 0);
>
> Nit but...
>
> Can we have a comment indicating what the last parameter refers to? I think
> David maybe doens't like this so obviously if he prefers not that fine, but
> I'm thinking something like:
>
> pte = get_and_clear_full_ptes(mm, old_addr, old_ptep, nr, /*full=*/false);
>
> I think we are good to just use 'false' here right? As it's only an int for
> historical purposes...
>
>> pte = move_pte(pte, old_addr, new_addr);
>> pte = move_soft_dirty_pte(pte);
>>
>> @@ -267,7 +290,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
>> else if (is_swap_pte(pte))
>> pte = pte_swp_clear_uffd_wp(pte);
>> }
>> - set_pte_at(mm, new_addr, new_ptep, pte);
>> + set_ptes(mm, new_addr, new_ptep, pte, nr);
>> }
>> }
>>
>> --
>> 2.30.2
>>
^ permalink raw reply [flat|nested] 23+ messages in thread* Re: [PATCH v2 2/2] mm: Optimize mremap() by PTE batching
2025-05-18 8:17 ` Dev Jain
@ 2025-05-19 9:04 ` Lorenzo Stoakes
2025-05-20 9:21 ` Dev Jain
0 siblings, 1 reply; 23+ messages in thread
From: Lorenzo Stoakes @ 2025-05-19 9:04 UTC (permalink / raw)
To: Dev Jain
Cc: akpm, Liam.Howlett, vbabka, jannh, pfalcato, linux-mm,
linux-kernel, david, peterx, ryan.roberts, mingo, libang.li,
maobibo, zhengqi.arch, baohua, anshuman.khandual, willy,
ioworker0, yang, baolin.wang, ziy, hughd
On Sun, May 18, 2025 at 01:47:35PM +0530, Dev Jain wrote:
>
>
> On 08/05/25 3:34 pm, Lorenzo Stoakes wrote:
> > Before getting into the review, just to say thanks for refactoring as per
> > my (and of course other's) comments, much appreciated and big improvement!
> > :)
> >
> > We're getting there...
> >
> > On Wed, May 07, 2025 at 11:32:56AM +0530, Dev Jain wrote:
> > > To use PTE batching, we want to determine whether the folio mapped by
> > > the PTE is large, thus requiring the use of vm_normal_folio(). We want
> > > to avoid the cost of vm_normal_folio() if the code path doesn't already
> > > require the folio. For arm64, pte_batch_hint() does the job. To generalize
> > > this hint, add a helper which will determine whether two consecutive PTEs
> > > point to consecutive PFNs, in which case there is a high probability that
> > > the underlying folio is large.
> > > Next, use folio_pte_batch() to optimize move_ptes(). On arm64, if the ptes
> > > are painted with the contig bit, then ptep_get() will iterate through all 16
> > > entries to collect a/d bits. Hence this optimization will result in a 16x
> > > reduction in the number of ptep_get() calls. Next, ptep_get_and_clear()
> > > will eventually call contpte_try_unfold() on every contig block, thus
> > > flushing the TLB for the complete large folio range. Instead, use
> > > get_and_clear_full_ptes() so as to elide TLBIs on each contig block, and only
> > > do them on the starting and ending contig block.
> > >
> > > Signed-off-by: Dev Jain <dev.jain@arm.com>
> > > ---
> > > include/linux/pgtable.h | 29 +++++++++++++++++++++++++++++
> > > mm/mremap.c | 37 ++++++++++++++++++++++++++++++-------
> > > 2 files changed, 59 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> > > index b50447ef1c92..38dab1f562ed 100644
> > > --- a/include/linux/pgtable.h
> > > +++ b/include/linux/pgtable.h
> > > @@ -369,6 +369,35 @@ static inline pgd_t pgdp_get(pgd_t *pgdp)
> > > }
> > > #endif
> > >
> > > +/**
> > > + * maybe_contiguous_pte_pfns - Hint whether the page mapped by the pte belongs
> > > + * to a large folio.
> > > + * @ptep: Pointer to the page table entry.
> > > + * @pte: The page table entry.
> > > + *
> > > + * This helper is invoked when the caller wants to batch over a set of ptes
> > > + * mapping a large folio, but the concerned code path does not already have
> > > + * the folio. We want to avoid the cost of vm_normal_folio() only to find that
> > > + * the underlying folio was small; i.e keep the small folio case as fast as
> > > + * possible.
> > > + *
> > > + * The caller must ensure that ptep + 1 exists.
> > > + */
> > > +static inline bool maybe_contiguous_pte_pfns(pte_t *ptep, pte_t pte)
> > > +{
> > > + pte_t *next_ptep, next_pte;
> > > +
> > > + if (pte_batch_hint(ptep, pte) != 1)
> > > + return true;
> > > +
> > > + next_ptep = ptep + 1;
> > > + next_pte = ptep_get(next_ptep);
> > > + if (!pte_present(next_pte))
> > > + return false;
> > > +
> > > + return unlikely(pte_pfn(next_pte) - pte_pfn(pte) == 1);
> >
> > Let's not do unlikely()'s unless we have data for them... it shouldn't mean
> > 'what the programmer believes' :)
> >
> > > +}
> >
> > Yeah I'm with Andrew and Anshuman, I mean this is kind of a nasty interface
> > (I mean _perhaps_ unavoidably) and we've done the relevant check in
> > mremap_folio_pte_batch(), so let's just move it there with comments, as this
> >
> > > +
> > > #ifndef __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
> > > static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
> > > unsigned long address,
> > > diff --git a/mm/mremap.c b/mm/mremap.c
> > > index 0163e02e5aa8..9c88a276bec4 100644
> > > --- a/mm/mremap.c
> > > +++ b/mm/mremap.c
> > > @@ -170,6 +170,23 @@ static pte_t move_soft_dirty_pte(pte_t pte)
> > > return pte;
> > > }
> > >
> > > +/* mremap a batch of PTEs mapping the same large folio */
> > > +static int mremap_folio_pte_batch(struct vm_area_struct *vma, unsigned long addr,
> > > + pte_t *ptep, pte_t pte, int max_nr)
> > > +{
> > > + const fpb_t flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
> > > + struct folio *folio;
> > > + int nr = 1;
> > > +
> > > + if ((max_nr != 1) && maybe_contiguous_pte_pfns(ptep, pte)) {
> > > + folio = vm_normal_folio(vma, addr, pte);
> > > + if (folio && folio_test_large(folio))
> > > + nr = folio_pte_batch(folio, addr, ptep, pte, max_nr,
> > > + flags, NULL, NULL, NULL);
> > > + }
> >
> > This needs some refactoring, avoid nesting at all costs :)
> >
> > We'll want to move the maybe_contiguous_pte_pfns() function over here, so
> > that'll change things, but in general let's use a guard clause.
> >
> > So an if block like:
> >
> > if (foo) {
> > ... bunch of logic ...
> > }
> >
> > Is better replaced with a guard clause so you have:
> >
> > if (!foo)
> > return ...;
> >
> > ... bunch of logic ...
> >
> > Here we could really expand things out to make things SUPER clear like:
> >
> > static int mremap_folio_pte_batch(struct vm_area_struct *vma, unsigned long addr,
> > pte_t *ptep, pte_t pte, int max_nr)
> > {
> > const fpb_t flags;
> > struct folio *folio;
> >
> > if (max_nr == 1)
> > return 1;
> > if (!maybe_contiguous_pte_pfns(ptep, pte)) // obviously replace with open code...
> > return 1;
> >
> > folio = vm_normal_folio(vma, addr, pte);
> > if (!folio)
> > return 1;
> > if (!folio_test_large(folio))
> > return 1;
> >
> > flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
> > return folio_pte_batch(folio, addr, ptep, pte, max_nr,
> > flags, NULL, NULL, NULL);
> > }
> >
> > I mean you could argue assign nr would be neater here, but you get the point!
> >
> > David mentioned a point about this code over in v1 discussion (see
> > [0]). Trying to bring converastion here to avoid it being split across
> > old/new series. There he said:
> >
> > David H:
> > > (2) Do we really need "must be part of the same folio", or could be just batch over present
> > > ptes that map consecutive PFNs? In that case, a helper that avoids folio_pte_batch() completely
> > > might be better.
> >
> > Hm, if we didn't do the batch test, can we batch a split large folio here ok?
> > I'm guessing we can in which case this check is actually limiting...
> >
> > Are we _explicitly_ only considering the cont pte case and ignoring the
> > split THP case?
> >
> > [0]: https://lore.kernel.org/all/887fb371-409e-4dad-b4ff-38b85bfddf95@redhat.com/
> >
> > And in what circumstances will the hint be set, with a present subsequent
> > PTE but !folio_test_large()?
> >
> > I guess the hint might not be taken? But then isn't the valid check just
> > folio_test_large() and we don't need this batched check at all?
> >
> > Is it only to avoid the split THP case?
> >
> > We definitely need some clarity here, and a comment in the code explaining
> > what's going on as this is subtle stuff.
>
> I am focussed only on batching large folios. Split THPs won't be batched;
> you can use pte_batch() (from David's refactoring) and
> figure the split THP batch out, but then get_and_clear_full_ptes()
> will be gathering a/d bits and smearing them across the batch, which will be
> incorrect. Even if we introduce a new version of get_and_clear_full_ptes()
> which does not gather a/d bits, then if the pte_batch actually belongs to a
> folio, then we will *not* be smearing a/d bits, which is again wrong. So in
> any case we must know what the underlying folio looks like :) So my agenda
> for v3 is,
Right, ack, there being a large folio per se doesn't mean A/D collection is
appropriate in THP case.
I guess then this is really _only_ about the mTHP case, where essentially
the other PTEs are to be disregarded going forwards?
>
> - Incorporate your refactoring comments
> - Remove maybe_contiguous_pte_pfns and just use vm_normal_folio +
> folio_test_large
> - Fix indentation
>
> Sounds good?
Sure, but can we hold off until the mprotect() stuff is done first please?
I mean obviously you're free to do things as you like, but this will help
workload-wise on my side :>)
Thanks!
>
> >
> > > + return nr;
> > > +}
> > > +
> > > static int move_ptes(struct pagetable_move_control *pmc,
> > > unsigned long extent, pmd_t *old_pmd, pmd_t *new_pmd)
> > > {
> > > @@ -177,7 +194,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
> > > bool need_clear_uffd_wp = vma_has_uffd_without_event_remap(vma);
> > > struct mm_struct *mm = vma->vm_mm;
> > > pte_t *old_ptep, *new_ptep;
> > > - pte_t pte;
> > > + pte_t old_pte, pte;
> > > pmd_t dummy_pmdval;
> > > spinlock_t *old_ptl, *new_ptl;
> > > bool force_flush = false;
> > > @@ -186,6 +203,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
> > > unsigned long old_end = old_addr + extent;
> > > unsigned long len = old_end - old_addr;
> > > int err = 0;
> > > + int max_nr;
> > >
> > > /*
> > > * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
> > > @@ -236,12 +254,13 @@ static int move_ptes(struct pagetable_move_control *pmc,
> > > flush_tlb_batched_pending(vma->vm_mm);
> > > arch_enter_lazy_mmu_mode();
> > >
> > > - for (; old_addr < old_end; old_ptep++, old_addr += PAGE_SIZE,
> > > - new_ptep++, new_addr += PAGE_SIZE) {
> > > - if (pte_none(ptep_get(old_ptep)))
> > > + for (int nr = 1; old_addr < old_end; old_ptep += nr, old_addr += nr * PAGE_SIZE,
> > > + new_ptep += nr, new_addr += nr * PAGE_SIZE) {
> >
> > Really nitty thing here but the indentation is all messed up here, I mean
> > nothing is going to be nice but maybe indent by two tabs below 'for'.
> >
> > I'm not a fan of this declaration of nr, typically in a for loop a declaration
> > here would be the counter, so this is just confusing.
> >
> > In the old implementation, declaring nr in the for loop would make sense,
> > but in the newly refactored one you should just declare it at the top.
> >
> > Also as per Anshuman review, I think nr_ptes, max_nr_ptes would be better.
> >
> > I don't think 'nr' needs to be initialised either, since the conditional is
> > 'old_addr < old_end' and you _should_ only perform the
> >
> > > + max_nr = (old_end - old_addr) >> PAGE_SHIFT;
> > > + old_pte = ptep_get(old_ptep);
> > > + if (pte_none(old_pte))
> >
> > This seems broken.
> >
> > You're missing a nr assignment here, so you'll happen to offset by the
> > number of pages of the last folio you encountered?
> >
> > Should be:
> >
> > if (pte_none(old_pte)) {
> > nr_ptes = 1;
> > continue;
> > }
> >
> > Or, alternatively, you can reset nr_ptes to 1 at the start of each loop.
> >
> >
> > > continue;
> > >
> > > - pte = ptep_get_and_clear(mm, old_addr, old_ptep);
> >
> > > /*
> > > * If we are remapping a valid PTE, make sure
> > > * to flush TLB before we drop the PTL for the
> > > @@ -253,8 +272,12 @@ static int move_ptes(struct pagetable_move_control *pmc,
> > > * the TLB entry for the old mapping has been
> > > * flushed.
> > > */
> > > - if (pte_present(pte))
> > > + if (pte_present(old_pte)) {
> > > + nr = mremap_folio_pte_batch(vma, old_addr, old_ptep,
> > > + old_pte, max_nr);
> > > force_flush = true;
> > > + }
> >
> > Thanks this is much clearer compared to v1
> >
> > > + pte = get_and_clear_full_ptes(mm, old_addr, old_ptep, nr, 0);
> >
> > Nit but...
> >
> > Can we have a comment indicating what the last parameter refers to? I think
> > David maybe doens't like this so obviously if he prefers not that fine, but
> > I'm thinking something like:
> >
> > pte = get_and_clear_full_ptes(mm, old_addr, old_ptep, nr, /*full=*/false);
> >
> > I think we are good to just use 'false' here right? As it's only an int for
> > historical purposes...
> >
> > > pte = move_pte(pte, old_addr, new_addr);
> > > pte = move_soft_dirty_pte(pte);
> > >
> > > @@ -267,7 +290,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
> > > else if (is_swap_pte(pte))
> > > pte = pte_swp_clear_uffd_wp(pte);
> > > }
> > > - set_pte_at(mm, new_addr, new_ptep, pte);
> > > + set_ptes(mm, new_addr, new_ptep, pte, nr);
> > > }
> > > }
> > >
> > > --
> > > 2.30.2
> > >
>
^ permalink raw reply [flat|nested] 23+ messages in thread* Re: [PATCH v2 2/2] mm: Optimize mremap() by PTE batching
2025-05-19 9:04 ` Lorenzo Stoakes
@ 2025-05-20 9:21 ` Dev Jain
0 siblings, 0 replies; 23+ messages in thread
From: Dev Jain @ 2025-05-20 9:21 UTC (permalink / raw)
To: Lorenzo Stoakes
Cc: akpm, Liam.Howlett, vbabka, jannh, pfalcato, linux-mm,
linux-kernel, david, peterx, ryan.roberts, mingo, libang.li,
maobibo, zhengqi.arch, baohua, anshuman.khandual, willy,
ioworker0, yang, baolin.wang, ziy, hughd
On 19/05/25 2:34 pm, Lorenzo Stoakes wrote:
> On Sun, May 18, 2025 at 01:47:35PM +0530, Dev Jain wrote:
>>
>>
>> On 08/05/25 3:34 pm, Lorenzo Stoakes wrote:
>>> Before getting into the review, just to say thanks for refactoring as per
>>> my (and of course other's) comments, much appreciated and big improvement!
>>> :)
>>>
>>> We're getting there...
>>>
>>> On Wed, May 07, 2025 at 11:32:56AM +0530, Dev Jain wrote:
>>>> To use PTE batching, we want to determine whether the folio mapped by
>>>> the PTE is large, thus requiring the use of vm_normal_folio(). We want
>>>> to avoid the cost of vm_normal_folio() if the code path doesn't already
>>>> require the folio. For arm64, pte_batch_hint() does the job. To generalize
>>>> this hint, add a helper which will determine whether two consecutive PTEs
>>>> point to consecutive PFNs, in which case there is a high probability that
>>>> the underlying folio is large.
>>>> Next, use folio_pte_batch() to optimize move_ptes(). On arm64, if the ptes
>>>> are painted with the contig bit, then ptep_get() will iterate through all 16
>>>> entries to collect a/d bits. Hence this optimization will result in a 16x
>>>> reduction in the number of ptep_get() calls. Next, ptep_get_and_clear()
>>>> will eventually call contpte_try_unfold() on every contig block, thus
>>>> flushing the TLB for the complete large folio range. Instead, use
>>>> get_and_clear_full_ptes() so as to elide TLBIs on each contig block, and only
>>>> do them on the starting and ending contig block.
>>>>
>>>> Signed-off-by: Dev Jain <dev.jain@arm.com>
>>>> ---
>>>> include/linux/pgtable.h | 29 +++++++++++++++++++++++++++++
>>>> mm/mremap.c | 37 ++++++++++++++++++++++++++++++-------
>>>> 2 files changed, 59 insertions(+), 7 deletions(-)
>>>>
>>>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
>>>> index b50447ef1c92..38dab1f562ed 100644
>>>> --- a/include/linux/pgtable.h
>>>> +++ b/include/linux/pgtable.h
>>>> @@ -369,6 +369,35 @@ static inline pgd_t pgdp_get(pgd_t *pgdp)
>>>> }
>>>> #endif
>>>>
>>>> +/**
>>>> + * maybe_contiguous_pte_pfns - Hint whether the page mapped by the pte belongs
>>>> + * to a large folio.
>>>> + * @ptep: Pointer to the page table entry.
>>>> + * @pte: The page table entry.
>>>> + *
>>>> + * This helper is invoked when the caller wants to batch over a set of ptes
>>>> + * mapping a large folio, but the concerned code path does not already have
>>>> + * the folio. We want to avoid the cost of vm_normal_folio() only to find that
>>>> + * the underlying folio was small; i.e keep the small folio case as fast as
>>>> + * possible.
>>>> + *
>>>> + * The caller must ensure that ptep + 1 exists.
>>>> + */
>>>> +static inline bool maybe_contiguous_pte_pfns(pte_t *ptep, pte_t pte)
>>>> +{
>>>> + pte_t *next_ptep, next_pte;
>>>> +
>>>> + if (pte_batch_hint(ptep, pte) != 1)
>>>> + return true;
>>>> +
>>>> + next_ptep = ptep + 1;
>>>> + next_pte = ptep_get(next_ptep);
>>>> + if (!pte_present(next_pte))
>>>> + return false;
>>>> +
>>>> + return unlikely(pte_pfn(next_pte) - pte_pfn(pte) == 1);
>>>
>>> Let's not do unlikely()'s unless we have data for them... it shouldn't mean
>>> 'what the programmer believes' :)
>>>
>>>> +}
>>>
>>> Yeah I'm with Andrew and Anshuman, I mean this is kind of a nasty interface
>>> (I mean _perhaps_ unavoidably) and we've done the relevant check in
>>> mremap_folio_pte_batch(), so let's just move it there with comments, as this
>>>
>>>> +
>>>> #ifndef __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
>>>> static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
>>>> unsigned long address,
>>>> diff --git a/mm/mremap.c b/mm/mremap.c
>>>> index 0163e02e5aa8..9c88a276bec4 100644
>>>> --- a/mm/mremap.c
>>>> +++ b/mm/mremap.c
>>>> @@ -170,6 +170,23 @@ static pte_t move_soft_dirty_pte(pte_t pte)
>>>> return pte;
>>>> }
>>>>
>>>> +/* mremap a batch of PTEs mapping the same large folio */
>>>> +static int mremap_folio_pte_batch(struct vm_area_struct *vma, unsigned long addr,
>>>> + pte_t *ptep, pte_t pte, int max_nr)
>>>> +{
>>>> + const fpb_t flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
>>>> + struct folio *folio;
>>>> + int nr = 1;
>>>> +
>>>> + if ((max_nr != 1) && maybe_contiguous_pte_pfns(ptep, pte)) {
>>>> + folio = vm_normal_folio(vma, addr, pte);
>>>> + if (folio && folio_test_large(folio))
>>>> + nr = folio_pte_batch(folio, addr, ptep, pte, max_nr,
>>>> + flags, NULL, NULL, NULL);
>>>> + }
>>>
>>> This needs some refactoring, avoid nesting at all costs :)
>>>
>>> We'll want to move the maybe_contiguous_pte_pfns() function over here, so
>>> that'll change things, but in general let's use a guard clause.
>>>
>>> So an if block like:
>>>
>>> if (foo) {
>>> ... bunch of logic ...
>>> }
>>>
>>> Is better replaced with a guard clause so you have:
>>>
>>> if (!foo)
>>> return ...;
>>>
>>> ... bunch of logic ...
>>>
>>> Here we could really expand things out to make things SUPER clear like:
>>>
>>> static int mremap_folio_pte_batch(struct vm_area_struct *vma, unsigned long addr,
>>> pte_t *ptep, pte_t pte, int max_nr)
>>> {
>>> const fpb_t flags;
>>> struct folio *folio;
>>>
>>> if (max_nr == 1)
>>> return 1;
>>> if (!maybe_contiguous_pte_pfns(ptep, pte)) // obviously replace with open code...
>>> return 1;
>>>
>>> folio = vm_normal_folio(vma, addr, pte);
>>> if (!folio)
>>> return 1;
>>> if (!folio_test_large(folio))
>>> return 1;
>>>
>>> flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
>>> return folio_pte_batch(folio, addr, ptep, pte, max_nr,
>>> flags, NULL, NULL, NULL);
>>> }
>>>
>>> I mean you could argue assign nr would be neater here, but you get the point!
>>>
>>> David mentioned a point about this code over in v1 discussion (see
>>> [0]). Trying to bring converastion here to avoid it being split across
>>> old/new series. There he said:
>>>
>>> David H:
>>>> (2) Do we really need "must be part of the same folio", or could be just batch over present
>>>> ptes that map consecutive PFNs? In that case, a helper that avoids folio_pte_batch() completely
>>>> might be better.
>>>
>>> Hm, if we didn't do the batch test, can we batch a split large folio here ok?
>>> I'm guessing we can in which case this check is actually limiting...
>>>
>>> Are we _explicitly_ only considering the cont pte case and ignoring the
>>> split THP case?
>>>
>>> [0]: https://lore.kernel.org/all/887fb371-409e-4dad-b4ff-38b85bfddf95@redhat.com/
>>>
>>> And in what circumstances will the hint be set, with a present subsequent
>>> PTE but !folio_test_large()?
>>>
>>> I guess the hint might not be taken? But then isn't the valid check just
>>> folio_test_large() and we don't need this batched check at all?
>>>
>>> Is it only to avoid the split THP case?
>>>
>>> We definitely need some clarity here, and a comment in the code explaining
>>> what's going on as this is subtle stuff.
>>
>> I am focussed only on batching large folios. Split THPs won't be batched;
>> you can use pte_batch() (from David's refactoring) and
>> figure the split THP batch out, but then get_and_clear_full_ptes()
>> will be gathering a/d bits and smearing them across the batch, which will be
>> incorrect. Even if we introduce a new version of get_and_clear_full_ptes()
>> which does not gather a/d bits, then if the pte_batch actually belongs to a
>> folio, then we will *not* be smearing a/d bits, which is again wrong. So in
>> any case we must know what the underlying folio looks like :) So my agenda
>> for v3 is,
>
> Right, ack, there being a large folio per se doesn't mean A/D collection is
> appropriate in THP case.
>
> I guess then this is really _only_ about the mTHP case, where essentially
> the other PTEs are to be disregarded going forwards?
Yes.
>
>>
>> - Incorporate your refactoring comments
>> - Remove maybe_contiguous_pte_pfns and just use vm_normal_folio +
>> folio_test_large
>> - Fix indentation
>>
>> Sounds good?
>
> Sure, but can we hold off until the mprotect() stuff is done first please?
> I mean obviously you're free to do things as you like, but this will help
> workload-wise on my side :>)
>
> Thanks!
No problem, thanks for reviewing!
>
>>
>>>
>>>> + return nr;
>>>> +}
>>>> +
>>>> static int move_ptes(struct pagetable_move_control *pmc,
>>>> unsigned long extent, pmd_t *old_pmd, pmd_t *new_pmd)
>>>> {
>>>> @@ -177,7 +194,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
>>>> bool need_clear_uffd_wp = vma_has_uffd_without_event_remap(vma);
>>>> struct mm_struct *mm = vma->vm_mm;
>>>> pte_t *old_ptep, *new_ptep;
>>>> - pte_t pte;
>>>> + pte_t old_pte, pte;
>>>> pmd_t dummy_pmdval;
>>>> spinlock_t *old_ptl, *new_ptl;
>>>> bool force_flush = false;
>>>> @@ -186,6 +203,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
>>>> unsigned long old_end = old_addr + extent;
>>>> unsigned long len = old_end - old_addr;
>>>> int err = 0;
>>>> + int max_nr;
>>>>
>>>> /*
>>>> * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
>>>> @@ -236,12 +254,13 @@ static int move_ptes(struct pagetable_move_control *pmc,
>>>> flush_tlb_batched_pending(vma->vm_mm);
>>>> arch_enter_lazy_mmu_mode();
>>>>
>>>> - for (; old_addr < old_end; old_ptep++, old_addr += PAGE_SIZE,
>>>> - new_ptep++, new_addr += PAGE_SIZE) {
>>>> - if (pte_none(ptep_get(old_ptep)))
>>>> + for (int nr = 1; old_addr < old_end; old_ptep += nr, old_addr += nr * PAGE_SIZE,
>>>> + new_ptep += nr, new_addr += nr * PAGE_SIZE) {
>>>
>>> Really nitty thing here but the indentation is all messed up here, I mean
>>> nothing is going to be nice but maybe indent by two tabs below 'for'.
>>>
>>> I'm not a fan of this declaration of nr, typically in a for loop a declaration
>>> here would be the counter, so this is just confusing.
>>>
>>> In the old implementation, declaring nr in the for loop would make sense,
>>> but in the newly refactored one you should just declare it at the top.
>>>
>>> Also as per Anshuman review, I think nr_ptes, max_nr_ptes would be better.
>>>
>>> I don't think 'nr' needs to be initialised either, since the conditional is
>>> 'old_addr < old_end' and you _should_ only perform the
>>>
>>>> + max_nr = (old_end - old_addr) >> PAGE_SHIFT;
>>>> + old_pte = ptep_get(old_ptep);
>>>> + if (pte_none(old_pte))
>>>
>>> This seems broken.
>>>
>>> You're missing a nr assignment here, so you'll happen to offset by the
>>> number of pages of the last folio you encountered?
>>>
>>> Should be:
>>>
>>> if (pte_none(old_pte)) {
>>> nr_ptes = 1;
>>> continue;
>>> }
>>>
>>> Or, alternatively, you can reset nr_ptes to 1 at the start of each loop.
>>>
>>>
>>>> continue;
>>>>
>>>> - pte = ptep_get_and_clear(mm, old_addr, old_ptep);
>>>
>>>> /*
>>>> * If we are remapping a valid PTE, make sure
>>>> * to flush TLB before we drop the PTL for the
>>>> @@ -253,8 +272,12 @@ static int move_ptes(struct pagetable_move_control *pmc,
>>>> * the TLB entry for the old mapping has been
>>>> * flushed.
>>>> */
>>>> - if (pte_present(pte))
>>>> + if (pte_present(old_pte)) {
>>>> + nr = mremap_folio_pte_batch(vma, old_addr, old_ptep,
>>>> + old_pte, max_nr);
>>>> force_flush = true;
>>>> + }
>>>
>>> Thanks this is much clearer compared to v1
>>>
>>>> + pte = get_and_clear_full_ptes(mm, old_addr, old_ptep, nr, 0);
>>>
>>> Nit but...
>>>
>>> Can we have a comment indicating what the last parameter refers to? I think
>>> David maybe doens't like this so obviously if he prefers not that fine, but
>>> I'm thinking something like:
>>>
>>> pte = get_and_clear_full_ptes(mm, old_addr, old_ptep, nr, /*full=*/false);
>>>
>>> I think we are good to just use 'false' here right? As it's only an int for
>>> historical purposes...
>>>
>>>> pte = move_pte(pte, old_addr, new_addr);
>>>> pte = move_soft_dirty_pte(pte);
>>>>
>>>> @@ -267,7 +290,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
>>>> else if (is_swap_pte(pte))
>>>> pte = pte_swp_clear_uffd_wp(pte);
>>>> }
>>>> - set_pte_at(mm, new_addr, new_ptep, pte);
>>>> + set_ptes(mm, new_addr, new_ptep, pte, nr);
>>>> }
>>>> }
>>>>
>>>> --
>>>> 2.30.2
>>>>
>>
^ permalink raw reply [flat|nested] 23+ messages in thread