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@xxxxxxxxxx>
---
Given the comments on not needing to hold mmap_lock it was not 100% clear
to me if it is safe to check vma->vma_flags & VM_LOCKED and if re-checking
under the ptl was significant. I left the extra check in case it was, but
it seems one of the checks is redunant as either the first check is racey
or the second check is unneccsary.
---
include/linux/rmap.h | 1 -
mm/rmap.c | 47 ++++++++++++++++++++++++++++++++++++--------
2 files changed, 39 insertions(+), 9 deletions(-)
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 70085ca1a3fc..7f1ee411bd7b 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 ef9ef2694c58..850eecdd866a 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1391,10 +1391,6 @@ 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;
@@ -1455,8 +1451,6 @@ 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? */
@@ -1775,6 +1769,44 @@ static int page_not_mapped(struct page *page)
return !page_mapped(page);
};
+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,
+ };
+ bool ret = true;
+
+ /* munlock has nothing to gain from examining un-locked vmas */
+ if (!(vma->vm_flags & VM_LOCKED))
+ return true;
+
+ while (page_vma_mapped_walk(&pvmw)) {
+ /*
+ * If the page is mlock()d, we cannot swap it out.
+ * If it's recently referenced (perhaps page_referenced
+ * skipped over this mm) then we should reactivate it.
+ */
+ if (vma->vm_flags & VM_LOCKED) {
+ /* PTE-mapped THP are never mlocked */
+ if (!PageTransCompound(page)) {
+ /*
+ * Holding pte lock, we do *not* need
+ * mmap_lock here
+ */
+ mlock_vma_page(page);
+ }
+ ret = false;
+ page_vma_mapped_walk_done(&pvmw);
+ break;
+ }
+ }
+
+ return ret;
+}
+
/**
* try_to_munlock - try to munlock a page
* @page: the page to be munlocked
@@ -1787,8 +1819,7 @@ static int page_not_mapped(struct page *page)
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
