diff mbox series

[to-be-updated] shmem-shmem_writepage-split-unlikely-i915-thp.patch removed from -mm tree

Message ID 20200922195822.34qJx%akpm@linux-foundation.org
State New
Headers show
Series [to-be-updated] shmem-shmem_writepage-split-unlikely-i915-thp.patch removed from -mm tree | expand

Commit Message

Andrew Morton Sept. 22, 2020, 7:58 p.m. UTC 
The patch titled
     Subject: shmem: shmem_writepage() split unlikely i915 THP
has been removed from the -mm tree.  Its filename was
     shmem-shmem_writepage-split-unlikely-i915-thp.patch

This patch was dropped because an updated version will be merged

------------------------------------------------------
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>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Yang Shi <shy828301@gmail.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: Matthew Wilcox <willy@infradead.org>
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(-)
diff mbox series

Patch

--- a/mm/shmem.c~shmem-shmem_writepage-split-unlikely-i915-thp
+++ a/mm/shmem.c
@@ -1364,7 +1364,15 @@  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;