The patch titled
mlock: avoid dirtying pages and triggering writeback
has been added to the -mm tree. Its filename is
mlock-avoid-dirtying-pages-and-triggering-writeback.patch
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------------------------------------------------------
Subject: mlock: avoid dirtying pages and triggering writeback
From: Michel Lespinasse <walken@xxxxxxxxxx>
When faulting in pages for mlock(), we want to break COW for anonymous or
file pages within VM_WRITABLE, non-VM_SHARED vmas. However, there is no
need to write-fault into VM_SHARED vmas since shared file pages can be
mlocked first and dirtied later, when/if they actually get written to.
Skipping the write fault is desirable, as we don't want to unnecessarily
cause these pages to be dirtied and queued for writeback.
Signed-off-by: Michel Lespinasse <walken@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Kosaki Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Nick Piggin <npiggin@xxxxxxxxx>
Cc: Theodore Tso <tytso@xxxxxxxxxx>
Cc: Michael Rubin <mrubin@xxxxxxxxxx>
Cc: Suleiman Souhlal <suleiman@xxxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 7 ++++++-
mm/mlock.c | 7 ++++++-
2 files changed, 12 insertions(+), 2 deletions(-)
diff -puN mm/memory.c~mlock-avoid-dirtying-pages-and-triggering-writeback mm/memory.c
--- a/mm/memory.c~mlock-avoid-dirtying-pages-and-triggering-writeback
+++ a/mm/memory.c
@@ -3324,7 +3324,12 @@ int make_pages_present(unsigned long add
vma = find_vma(current->mm, addr);
if (!vma)
return -ENOMEM;
- write = (vma->vm_flags & VM_WRITE) != 0;
+ /*
+ * We want to touch writable mappings with a write fault in order
+ * to break COW, except for shared mappings because these don't COW
+ * and we would not want to dirty them for nothing.
+ */
+ write = (vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE;
BUG_ON(addr >= end);
BUG_ON(end > vma->vm_end);
len = DIV_ROUND_UP(end, PAGE_SIZE) - addr/PAGE_SIZE;
diff -puN mm/mlock.c~mlock-avoid-dirtying-pages-and-triggering-writeback mm/mlock.c
--- a/mm/mlock.c~mlock-avoid-dirtying-pages-and-triggering-writeback
+++ a/mm/mlock.c
@@ -171,7 +171,12 @@ static long __mlock_vma_pages_range(stru
VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
gup_flags = FOLL_TOUCH | FOLL_GET;
- if (vma->vm_flags & VM_WRITE)
+ /*
+ * We want to touch writable mappings with a write fault in order
+ * to break COW, except for shared mappings because these don't COW
+ * and we would not want to dirty them for nothing.
+ */
+ if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
gup_flags |= FOLL_WRITE;
/* We don't try to access the guard page of a stack vma */
_
Patches currently in -mm which might be from walken@xxxxxxxxxx are
do_wp_page-remove-the-reuse-flag.patch
do_wp_page-clarify-dirty_page-handling.patch
mlock-avoid-dirtying-pages-and-triggering-writeback.patch
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