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-unlikel... and later at http://ozlabs.org/~akpm/mmotm/broken-out/shmem-shmem_writepage-split-unlikel...

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------------------------------------------------------ From: Hugh Dickins hughd@google.com 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@google.com Cc: Alex Shi alex.shi@linux.alibaba.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: Michal Hocko mhocko@suse.com Cc: Mike Kravetz mike.kravetz@oracle.com Cc: Qian Cai cai@lca.pw Cc: Shakeel Butt shakeelb@google.com Cc: stable@vger.kernel.org [5.3+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

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@google.com 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