From: Oscar Salvador <osalvador@suse.de>
To: "Vishal Moola (Oracle)" <vishal.moola@gmail.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
akpm@linux-foundation.org, muchun.song@linux.dev,
Miaohe Lin <linmiaohe@huawei.com>
Subject: Re: [PATCH] mm/compaction: Fix bug in hugetlb handling pathway
Date: Tue, 1 Apr 2025 16:59:46 +0200 [thread overview]
Message-ID: <Z-v_YnBV_XJ89NnO@localhost.localdomain> (raw)
In-Reply-To: <20250401021025.637333-1-vishal.moola@gmail.com>
On Mon, Mar 31, 2025 at 07:10:24PM -0700, Vishal Moola (Oracle) wrote:
> The compaction code doesn't take references on pages until we're certain
> we should attempt to handle it.
>
> In the hugetlb case, isolate_or_dissolve_huge_page() may return -EBUSY
> without taking a reference to the folio associated with our pfn. If our
> folio's refcount drops to 0, compound_nr() becomes unpredictable, making
> low_pfn and nr_scanned unreliable.
> The user-visible effect is minimal - this should rarely happen (if ever).
So, with compound_order() we either return the real order of the
compound page or '0', right?
> Fix this by storing the folio statistics earlier on the stack (just like
> the THP and Buddy cases).
>
> Also revert commit 66fe1cf7f581 ("mm: compaction: use helper compound_nr
> in isolate_migratepages_block")
> to make backporting easier.
>
> Fixes: 369fa227c219 ("mm: make alloc_contig_range handle free hugetlb pages")
> Cc: Miaohe Lin <linmiaohe@huawei.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Acked-by: Oscar Salvador <osalvador@suse.de>
--
Oscar Salvador
SUSE Labs
next prev parent reply other threads:[~2025-04-01 14:59 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-04-01 2:10 Vishal Moola (Oracle)
2025-04-01 2:10 ` [PATCH] mm/compaction: Use folio in hugetlb pathway Vishal Moola (Oracle)
2025-04-01 15:04 ` Oscar Salvador
2025-04-01 15:23 ` Zi Yan
2025-04-01 14:59 ` Oscar Salvador [this message]
2025-04-01 17:55 ` [PATCH] mm/compaction: Fix bug in hugetlb handling pathway Vishal Moola (Oracle)
2025-04-01 15:20 ` Zi Yan
2025-04-01 18:09 ` Vishal Moola (Oracle)
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