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Date: Tue, 13 May 2025 10:11:49 +0200
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Huacai Chen <chenhuacai@loongson.cn>
Cc: Sasha Levin <sashal@kernel.org>, Huacai Chen <chenhuacai@kernel.org>,
	Xuerui Wang <kernel@xen0n.name>, stable@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
	loongarch@lists.linux.dev, Zi Yan <ziy@nvidia.com>,
	Huang Ying <ying.huang@intel.com>,
	Baolin Wang <baolin.wang@linux.alibaba.com>,
	David Hildenbrand <david@redhat.com>,
	Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH for 6.6] mm/migrate: correct nr_failed in
 migrate_pages_sync()
Message-ID: <2025051322-aftermost-puritan-fd62@gregkh>
References: <20250513080521.252543-1-chenhuacai@loongson.cn>
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In-Reply-To: <20250513080521.252543-1-chenhuacai@loongson.cn>

On Tue, May 13, 2025 at 04:05:21PM +0800, Huacai Chen wrote:
> From: Zi Yan <ziy@nvidia.com>
> 
> nr_failed was missing the large folio splits from migrate_pages_batch()
> and can cause a mismatch between migrate_pages() return value and the
> number of not migrated pages, i.e., when the return value of
> migrate_pages() is 0, there are still pages left in the from page list.
> It will happen when a non-PMD THP large folio fails to migrate due to
> -ENOMEM and is split successfully but not all the split pages are not
> migrated, migrate_pages_batch() would return non-zero, but
> astats.nr_thp_split = 0.  nr_failed would be 0 and returned to the caller
> of migrate_pages(), but the not migrated pages are left in the from page
> list without being added back to LRU lists.
> 
> Fix it by adding a new nr_split counter for large folio splits and adding
> it to nr_failed in migrate_page_sync() after migrate_pages_batch() is
> done.
> 
> Link: https://lkml.kernel.org/r/20231017163129.2025214-1-zi.yan@sent.com
> Fixes: 2ef7dbb26990 ("migrate_pages: try migrate in batch asynchronously firstly")
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> Acked-by: Huang Ying <ying.huang@intel.com>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Matthew Wilcox <willy@infradead.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
> ---
> This patch has a Fixes tag and should be backported to 6.6, I don't know
> why hasn't bakported.

Because "Fixes:" never means that it will be backported.  Please read
the stable documentation for what needs to be added to ensure that.

thanks,

greg k-h