diff options
author | Hugh Dickins <hughd@google.com> | 2021-09-03 00:54:43 +0300 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2021-09-03 19:58:12 +0300 |
commit | 1e6decf30af5c5c75445ed6ad4e65a26de578a03 (patch) | |
tree | 39a8c8a90831ad4b6762283c62219483d8a156de | |
parent | a7fddc36299a8a99073e9e6e922b6cd451508385 (diff) |
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 "always" (intended to be usable) or "force" (forces huge everywhere
for easy 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().
Patch history: when first sent last year
http://lkml.kernel.org/r/alpine.LSU.2.11.2008301401390.5954@eggly.anvils
https://lore.kernel.org/linux-mm/20200919042009.bomzxmrg7%25akpm@linux-foundation.org/
Matthew Wilcox noticed that tail pages were wrongly left clean. This
version brackets the split with Set and Clear PageDirty as he suggested:
which works very well, even if it falls short of our aspirations. And
recently I realized that the crash is not limited to the testing option
"force", but affects "always" too: which is more important to fix.
Link: https://lkml.kernel.org/r/bac6158c-8b3d-4dca-cffc-4982f58d9794@google.com
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: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r-- | mm/shmem.c | 14 |
1 files changed, 13 insertions, 1 deletions
diff --git a/mm/shmem.c b/mm/shmem.c index 69aa932c08da..21c29f7e3894 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1344,7 +1344,19 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc) swp_entry_t swap; pgoff_t index; - VM_BUG_ON_PAGE(PageCompound(page), page); + /* + * If /sys/kernel/mm/transparent_hugepage/shmem_enabled is "always" or + * "force", 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)) { + /* Ensure the subpages are still dirty */ + SetPageDirty(page); + if (split_huge_page(page) < 0) + goto redirty; + ClearPageDirty(page); + } + BUG_ON(!PageLocked(page)); mapping = page->mapping; index = page->index; |