When a transparent hugepage is mapped and it is included in an mlock()
range, follow_page() incorrectly avoids setting the page's mlock bit and
moving it to the unevictable lru.
This is evident if you try to mlock(), munlock(), and then mlock() a
range again. Currently:
#define MAP_SIZE (4 << 30) /* 4GB */
void *ptr = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
mlock(ptr, MAP_SIZE);
$ grep -E "Unevictable|Inactive\(anon" /proc/meminfo
Inactive(anon): 6304 kB
Unevictable: 4213924 kB
munlock(ptr, MAP_SIZE);
Inactive(anon): 4186252 kB
Unevictable: 19652 kB
mlock(ptr, MAP_SIZE);
Inactive(anon): 4198556 kB
Unevictable: 21684 kB
Notice that less than 2MB was added to the unevictable list; this is
because these pages in the range are not transparent hugepages since the
4GB range was allocated with mmap() and has no specific alignment. If
posix_memalign() were used instead, unevictable would not have grown at
all on the second mlock().
The fix is to call mlock_vma_page() so that the mlock bit is set and the
page is added to the unevictable list. With this patch:
mlock(ptr, MAP_SIZE);
Inactive(anon): 4056 kB
Unevictable: 4213940 kB
munlock(ptr, MAP_SIZE);
Inactive(anon): 4198268 kB
Unevictable: 19636 kB
mlock(ptr, MAP_SIZE);
Inactive(anon): 4008 kB
Unevictable: 4213940 kB
Cc: sta...@vger.kernel.org [v2.6.38+]
Signed-off-by: David Rientjes <rient...@google.com>
---
include/linux/huge_mm.h | 2 +-
mm/huge_memory.c | 11 ++++++++++-
mm/memory.c | 2 +-
3 files changed, 12 insertions(+), 3 deletions(-)
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -12,7 +12,7 @@ extern int do_huge_pmd_wp_page(struct mm_struct *mm, struct
vm_area_struct *vma,
unsigned long address, pmd_t *pmd,
pmd_t orig_pmd);
extern pgtable_t get_pmd_huge_pte(struct mm_struct *mm);
-extern struct page *follow_trans_huge_pmd(struct mm_struct *mm,
+extern struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
unsigned long addr,
pmd_t *pmd,
unsigned int flags);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -997,11 +997,12 @@ out:
return ret;
}
-struct page *follow_trans_huge_pmd(struct mm_struct *mm,
+struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
unsigned long addr,
pmd_t *pmd,
unsigned int flags)
{
+ struct mm_struct *mm = vma->vm_mm;
struct page *page = NULL;
assert_spin_locked(&mm->page_table_lock);
@@ -1024,6 +1025,14 @@ struct page *follow_trans_huge_pmd(struct mm_struct *mm,
_pmd = pmd_mkyoung(pmd_mkdirty(*pmd));
set_pmd_at(mm, addr & HPAGE_PMD_MASK, pmd, _pmd);
}
+ if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
+ if (page->mapping && trylock_page(page)) {
+ lru_add_drain();
+ if (page->mapping)
+ mlock_vma_page(page);
+ unlock_page(page);
+ }
+ }
page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
VM_BUG_ON(!PageCompound(page));
if (flags & FOLL_GET)
diff --git a/mm/memory.c b/mm/memory.c
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1521,7 +1521,7 @@ struct page *follow_page(struct vm_area_struct *vma,
unsigned long address,
spin_unlock(&mm->page_table_lock);
wait_split_huge_page(vma->anon_vma, pmd);
} else {
- page = follow_trans_huge_pmd(mm, address,
+ page = follow_trans_huge_pmd(vma, address,
pmd, flags);
spin_unlock(&mm->page_table_lock);
goto out;
--
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