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mm/khugepaged: collapse_shmem() stop if punched or truncated

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commit 701270fa193aadf00bdcf607738f64997275d4c7 upstream.

Huge tmpfs testing showed that although collapse_shmem() recognizes a
concurrently truncated or hole-punched page correctly, its handling of
holes was liable to refill an emptied extent.  Add check to stop that.

Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1811261522040.2275@eggly.anvils
Fixes: f3f0e1d2150b2 ("khugepaged: add support of collapse for tmpfs/shmem pages")
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Matthew Wilcox <willy@infradead.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: <stable@vger.kernel.org>	[4.8+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Hugh Dickins 2018-11-30 14:10:25 -08:00 committed by Greg Kroah-Hartman
parent 6f75a09833
commit 81d2848c99
1 changed files with 15 additions and 0 deletions
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15
mm/khugepaged.c
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@ -1352,6 +1352,16 @@ static void collapse_shmem(struct mm_struct *mm,
radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
int n = min(iter.index, end) - index;
/*
* Stop if extent has been hole-punched, and is now completely
* empty (the more obvious i_size_read() check would take an
* irq-unsafe seqlock on 32-bit).
*/
if (n >= HPAGE_PMD_NR) {
result = SCAN_TRUNCATED;
goto tree_locked;
}
/*
* Handle holes in the radix tree: charge it from shmem and
* insert relevant subpage of new_page into the radix-tree.
@ -1463,6 +1473,11 @@ out_unlock:
if (result == SCAN_SUCCEED && index < end) {
int n = end - index;
/* Stop if extent has been truncated, and is now empty */
if (n >= HPAGE_PMD_NR) {
result = SCAN_TRUNCATED;
goto tree_locked;
}
if (!shmem_charge(mapping->host, n)) {
result = SCAN_FAIL;
goto tree_locked;