linux-kernel - Re: [PATCH v3 1/2] mm/migrate: correct nr_failed in migrate_pages

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Message-ID: <b579dcff-044a-c75b-5186-d48b497af792@linux.alibaba.com>
Date:   Thu, 19 Oct 2023 19:04:14 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     Zi Yan <ziy@...dia.com>, Huang Ying <ying.huang@...el.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH v3 1/2] mm/migrate: correct nr_failed in
 migrate_pages_sync()



On 10/18/2023 12:31 AM, Zi Yan wrote:
> From: Zi Yan <ziy@...dia.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.
> 
> Fixes: 2ef7dbb26990 ("migrate_pages: try migrate in batch asynchronously firstly")
> Signed-off-by: Zi Yan <ziy@...dia.com>
> Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Huang Ying <ying.huang@...el.com>
> Cc: Matthew Wilcox <willy@...radead.org>
> ---

LGTM. Feel free to add:
Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>