Commit 8797f2f4 authored Nov 30, 2018 by Hugh Dickins Committed by Greg Kroah-Hartman Dec 05, 2018

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

commit 701270fa 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: f3f0e1d2 ("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>

parent d31ff472

mm/khugepaged.c

+15 −0

Original line number	Diff line number	Diff line
		@@ -1349,6 +1349,16 @@ static void collapse_shmem(struct mm_struct *mm,
		radix_tree_for_each_slot(slot, &mapping->i_pages, &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.
		@@ -1459,6 +1469,11 @@ static void collapse_shmem(struct mm_struct *mm,
		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;