The patch titled
Subject: shmem: shmem_writepage() split unlikely i915 THP
has been added to the -mm tree. Its filename is
shmem-shmem_writepage-split-unlikely-i915-thp.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/shmem-shmem_writepage-split-unlikely-i915-thp.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/shmem-shmem_writepage-split-unlikely-i915-thp.patch
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From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: shmem: shmem_writepage() split unlikely i915 THP
drivers/gpu/drm/i915/gem/i915_gem_shmem.c contains a shmem_writeback()
which calls shmem_writepage() from a shrinker: that usually works well
enough; but if /sys/kernel/mm/transparent_hugepage/shmem_enabled has been
set to "force" (documented as "Force the huge option on for all - very
useful for testing"), shmem_writepage() is surprised to be called with a
huge page, and crashes on the VM_BUG_ON_PAGE(PageCompound) (I did not find
out where the crash happens when CONFIG_DEBUG_VM is off).
LRU page reclaim always splits the shmem huge page first: I'd prefer not
to demand that of i915, so check and split compound in shmem_writepage().
Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2008301401390.5954@eggly.anvils
Fixes: 2d6692e642e7 ("drm/i915: Start writeback from the shrinker")
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Qian Cai <cai@xxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [5.3+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/shmem.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
--- a/mm/shmem.c~shmem-shmem_writepage-split-unlikely-i915-thp
+++ a/mm/shmem.c
@@ -1362,7 +1362,15 @@ static int shmem_writepage(struct page *
swp_entry_t swap;
pgoff_t index;
- VM_BUG_ON_PAGE(PageCompound(page), page);
+ /*
+ * If /sys/kernel/mm/transparent_hugepage/shmem_enabled is "force",
+ * then drivers/gpu/drm/i915/gem/i915_gem_shmem.c gets huge pages,
+ * and its shmem_writeback() needs them to be split when swapping.
+ */
+ if (PageTransCompound(page))
+ if (split_huge_page(page) < 0)
+ goto redirty;
+
BUG_ON(!PageLocked(page));
mapping = page->mapping;
index = page->index;
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
ksm-reinstate-memcg-charge-on-copied-pages.patch
mm-migration-of-hugetlbfs-page-skip-memcg.patch
shmem-shmem_writepage-split-unlikely-i915-thp.patch
mm-fix-check_move_unevictable_pages-on-thp.patch
mlock-fix-unevictable_pgs-event-counts-on-thp.patch
