From: Oscar Salvador <osalvador@suse.de>
To: Kairui Song <kasong@tencent.com>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
David Hildenbrand <david@redhat.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/memory: fix mapcount / refcount sanity check for mTHP reuse
Date: Mon, 28 Apr 2025 10:21:11 +0200 [thread overview]
Message-ID: <aA86d6L6GhAjnri1@localhost.localdomain> (raw)
In-Reply-To: <20250425074325.61833-1-ryncsn@gmail.com>
On Fri, Apr 25, 2025 at 03:43:25PM +0800, Kairui Song wrote:
> From: Kairui Song <kasong@tencent.com>
>
> The following WARNING was triggered during swap stress test with
> mTHP enabled:
...
> The WARN_ON here is simply incorrect. The refcount here must be at least
> the mapcount, not the opposite. Each mapcount must have a corresponding
> refcount, but the refcount may increase if other components grab the
> folio, which is acceptable. Meanwhile, having a mapcount larger than
> refcount is a real problem.
>
> So fix the WARN_ON condition.
>
> Fixes: 1da190f4d0a6 ("mm: Copy-on-Write (COW) reuse support for PTE-mapped THP")
> Reported-by: Kairui Song <kasong@tencent.com>
> Closes: https://lore.kernel.org/all/CAMgjq7D+ea3eg9gRCVvRnto3Sv3_H3WVhupX4e=k8T5QAfBHbw@mail.gmail.com/
> Suggested-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Kairui Song <kasong@tencent.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
--
Oscar Salvador
SUSE Labs
next prev parent reply other threads:[~2025-04-28 8:21 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-04-25 7:43 [PATCH] mm/memory: fix mapcount / refcount sanity check for mTHP reuse Kairui Song
2025-04-25 8:03 ` David Hildenbrand
2025-04-28 8:21 ` Oscar Salvador [this message]
2025-04-28 11:39 ` Anshuman Khandual
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