LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Hugh Dickins <hughd@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>,
	Shakeel Butt <shakeelb@google.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Yang Shi <shy828301@gmail.com>, Miaohe Lin <linmiaohe@huawei.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Michal Hocko <mhocko@suse.com>, Rik van Riel <riel@surriel.com>,
	Matthew Wilcox <willy@infradead.org>,
	Chris Wilson <chris@chris-wilson.co.uk>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: [PATCH 9/9] shmem: shmem_writepage() split unlikely i915 THP
Date: Tue, 17 Aug 2021 01:28:56 -0700 (PDT)	[thread overview]
Message-ID: <bac6158c-8b3d-4dca-cffc-4982f58d9794@google.com> (raw)
In-Reply-To: <da632211-8e3e-6b1-aee-ab24734429a0@google.com>

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.

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>
---
 mm/shmem.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index b60a7abff27d..a1ba03f39eaa 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1349,7 +1349,19 @@ 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;
-- 
2.26.2


      parent reply	other threads:[~2021-08-17  8:29 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-17  8:03 [PATCH 0/9] huge tmpfs: shmem_is_huge() fixes and cleanups Hugh Dickins
2021-08-17  8:06 ` [PATCH 1/9] huge tmpfs: fix fallocate(vanilla) advance over huge pages Hugh Dickins
2021-08-17  8:08 ` [PATCH 2/9] huge tmpfs: fix split_huge_page() after FALLOC_FL_KEEP_SIZE Hugh Dickins
2021-08-17  8:10 ` [PATCH 3/9] huge tmpfs: remove shrinklist addition from shmem_setattr() Hugh Dickins
2021-08-17  8:12 ` [PATCH 4/9] huge tmpfs: revert shmem's use of transhuge_vma_enabled() Hugh Dickins
2021-08-17  8:14 ` [PATCH 5/9] huge tmpfs: move shmem_huge_enabled() upwards Hugh Dickins
2021-08-17  8:17 ` [PATCH 6/9] huge tmpfs: SGP_NOALLOC to stop collapse_file() on race Hugh Dickins
2021-08-17 20:14   ` Yang Shi
2021-08-17  8:19 ` [PATCH 7/9] huge tmpfs: shmem_is_huge(vma, inode, index) Hugh Dickins
2021-08-17 20:16   ` Yang Shi
2021-08-17  8:22 ` [PATCH 8/9] huge tmpfs: decide stat.st_blksize by shmem_is_huge() Hugh Dickins
2021-08-17  8:28 ` Hugh Dickins [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=bac6158c-8b3d-4dca-cffc-4982f58d9794@google.com \
    --to=hughd@google.com \
    --cc=akpm@linux-foundation.org \
    --cc=chris@chris-wilson.co.uk \
    --cc=kirill.shutemov@linux.intel.com \
    --cc=linmiaohe@huawei.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=mhocko@suse.com \
    --cc=mike.kravetz@oracle.com \
    --cc=riel@surriel.com \
    --cc=shakeelb@google.com \
    --cc=shy828301@gmail.com \
    --cc=willy@infradead.org \
    --subject='Re: [PATCH 9/9] shmem: shmem_writepage() split unlikely i915 THP' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).