[PATCH v5 3/8] mm/rmap: Split try_to_munlock from try_to_unmap

Alistair Popple
2021-03-09T12:16:38Z

The behaviour of try_to_unmap_one() is difficult to follow because it
performs different operations based on a fairly large set of flags used
in different combinations.

TTU_MUNLOCK is one such flag. However it is exclusively used by
try_to_munlock() which specifies no other flags. Therefore rather than
overload try_to_unmap_one() with unrelated behaviour split this out into
it's own function and remove the flag.

Signed-off-by: Alistair Popple <apopple@nvidia.com>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>

---

Christoph - I didn't add your Reviewed-by from v3 because removal of the
extra VM_LOCKED check in v4 changed things slightly. Let me know if
you're still ok for me to add it. Thanks.

v4:
* Removed redundant check for VM_LOCKED
---
include/linux/rmap.h | 1 -
mm/rmap.c | 40 ++++++++++++++++++++++++++++++++--------
2 files changed, 32 insertions(+), 9 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index def5c62c93b3..e26ac2d71346 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -87,7 +87,6 @@ struct anon_vma_chain {

enum ttu_flags {
TTU_MIGRATION = 0x1, /* migration mode */
- TTU_MUNLOCK = 0x2, /* munlock mode */

TTU_SPLIT_HUGE_PMD = 0x4, /* split huge PMD if any */
TTU_IGNORE_MLOCK = 0x8, /* ignore mlock */
diff --git a/mm/rmap.c b/mm/rmap.c
index 977e70803ed8..d02bade5245b 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1405,10 +1405,6 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
struct mmu_notifier_range range;
enum ttu_flags flags = (enum ttu_flags)(long)arg;

- /* munlock has nothing to gain from examining un-locked vmas */
- if ((flags & TTU_MUNLOCK) && !(vma->vm_flags & VM_LOCKED))
- return true;
-
if (IS_ENABLED(CONFIG_MIGRATION) && (flags & TTU_MIGRATION) &&
is_zone_device_page(page) && !is_device_private_page(page))
return true;
@@ -1469,8 +1465,6 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
page_vma_mapped_walk_done(&pvmw);
break;
}
- if (flags & TTU_MUNLOCK)
- continue;
}

/* Unexpected PMD-mapped THP? */
@@ -1784,6 +1778,37 @@ bool try_to_unmap(struct page *page, enum ttu_flags flags)
return !page_mapcount(page) ? true : false;
}

+static bool try_to_munlock_one(struct page *page, struct vm_area_struct *vma,
+ unsigned long address, void *arg)
+{
+ struct page_vma_mapped_walk pvmw = {
+ .page = page,
+ .vma = vma,
+ .address = address,
+ };
+
+ /* munlock has nothing to gain from examining un-locked vmas */
+ if (!(vma->vm_flags & VM_LOCKED))
+ return true;
+
+ while (page_vma_mapped_walk(&pvmw)) {
+ /* PTE-mapped THP are never mlocked */
+ if (!PageTransCompound(page)) {
+ /*
+ * Holding pte lock, we do *not* need
+ * mmap_lock here
+ */
+ mlock_vma_page(page);
+ }
+ page_vma_mapped_walk_done(&pvmw);
+
+ /* found a mlocked page, no point continuing munlock check */
+ return false;
+ }
+
+ return true;
+}
+
/**
* try_to_munlock - try to munlock a page
* @page: the page to be munlocked
@@ -1796,8 +1821,7 @@ bool try_to_unmap(struct page *page, enum ttu_flags flags)
void try_to_munlock(struct page *page)
{
struct rmap_walk_control rwc = {
- .rmap_one = try_to_unmap_one,
- .arg = (void *)TTU_MUNLOCK,
+ .rmap_one = try_to_munlock_one,
.done = page_not_mapped,
.anon_lock = page_lock_anon_vma_read,

--
2.20.1