The patch titled
holepunch: fix disconnected pages after second truncate
has been added to the -mm tree. Its filename is
holepunch-fix-disconnected-pages-after-second-truncate.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
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------------------------------------------------------
Subject: holepunch: fix disconnected pages after second truncate
From: Hugh Dickins <hugh@xxxxxxxxxxx>
shmem_truncate_range has its own truncate_inode_pages_range, to free any pages
racily instantiated while it was in progress: a SHMEM_PAGEIN flag is set when
this might have happened. But holepunching gets no chance to clear that flag
at the start of vmtruncate_range, so it's always set (unless a truncate came
just before), so holepunch almost always does this second
truncate_inode_pages_range.
shmem holepunch has unlikely swap<->file races hereabouts whatever we do
(without a fuller rework than is fit for this release): I was going to skip
the second truncate in the punch_hole case, but Miklos points out that would
make holepunch correctness more vulnerable to swapoff. So keep the second
truncate, but follow it by an unmap_mapping_range to eliminate the
disconnected pages (freed from pagecache while still mapped in userspace) that
it might have left behind.
Signed-off-by: Hugh Dickins <hugh@xxxxxxxxxxx>
Cc: Miklos Szeredi <mszeredi@xxxxxxx>
Cc: Badari Pulavarty <pbadari@xxxxxxxxxx>
Cc: Nick Piggin <npiggin@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/shmem.c | 8 ++++++++
1 files changed, 8 insertions(+)
diff -puN mm/shmem.c~holepunch-fix-disconnected-pages-after-second-truncate mm/shmem.c
--- a/mm/shmem.c~holepunch-fix-disconnected-pages-after-second-truncate
+++ a/mm/shmem.c
@@ -674,8 +674,16 @@ done2:
* generic_delete_inode did it, before we lowered next_index.
* Also, though shmem_getpage checks i_size before adding to
* cache, no recheck after: so fix the narrow window there too.
+ *
+ * Recalling truncate_inode_pages_range and unmap_mapping_range
+ * every time for punch_hole (which never got a chance to clear
+ * SHMEM_PAGEIN at the start of vmtruncate_range) is expensive,
+ * yet hardly ever necessary: try to optimize them out later.
*/
truncate_inode_pages_range(inode->i_mapping, start, end);
+ if (punch_hole)
+ unmap_mapping_range(inode->i_mapping, start,
+ end - start, 1);
}
spin_lock(&info->lock);
_
Patches currently in -mm which might be from hugh@xxxxxxxxxxx are
holepunch-fix-shmem_truncate_range-punching-too-far.patch
holepunch-fix-shmem_truncate_range-punch-locking.patch
holepunch-fix-disconnected-pages-after-second-truncate.patch
holepunch-fix-mmap_sem-i_mutex-deadlock.patch
git-drm.patch
mm-more-rmap-checking.patch
mm-make-read_cache_page-synchronous.patch
fs-buffer-dont-pageuptodate-without-page-locked.patch
free-swap-space-of-reactivated-pages.patch
add-__gfp_movable-for-callers-to-flag-allocations-from-high-memory-that-may-be-migrated.patch
i386-add-ptep_test_and_clear_dirtyyoung.patch
i386-use-pte_update_defer-in-ptep_test_and_clear_dirtyyoung.patch
i386-use-pte_update_defer-in-ptep_test_and_clear_dirtyyoung-fix.patch
smaps-extract-pmd-walker-from-smaps-code.patch
smaps-add-pages-referenced-count-to-smaps.patch
smaps-add-clear_refs-file-to-clear-reference.patch
smaps-add-clear_refs-file-to-clear-reference-fix.patch
smaps-add-clear_refs-file-to-clear-reference-fix-fix-2.patch
smaps-use-ptep_test_and_clear_young.patch
tty-in-tiocsctty-when-we-steal-a-tty-hang-it-up-fix.patch
ext2-reservations.patch
ext2-balloc-use-io_error-label.patch
add-__gfp_movable-for-callers-to-flag-allocations-from-high-memory-that-may-be-migrated-swap-prefetch.patch
mm-only-free-swap-space-of-reactivated-pages-debug.patch
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