linux-kernel - Re: [PATCH] mm/migrate: Putback split folios when numa hint migration fails

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Message-Id: <D2KHSYKMJEYO.2EY10FZM8H2YM@nvidia.com>
Date: Mon, 08 Jul 2024 17:58:14 -0400
From: "Zi Yan" <ziy@...dia.com>
To: "Peter Xu" <peterx@...hat.com>, <linux-mm@...ck.org>,
 <linux-kernel@...r.kernel.org>
Cc: "Andrew Morton" <akpm@...ux-foundation.org>, "Yang Shi"
 <shy828301@...il.com>, "Hugh Dickins" <hughd@...gle.com>, "Baolin Wang"
 <baolin.wang@...ux.alibaba.com>, "Huang Ying" <ying.huang@...el.com>,
 "David Hildenbrand" <david@...hat.com>
Subject: Re: [PATCH] mm/migrate: Putback split folios when numa hint
 migration fails

On Mon Jul 8, 2024 at 5:55 PM EDT, Peter Xu wrote:
> This issue is not from any report yet, but by code observation only.
>
> This is yet another fix besides Hugh's patch [1] but on relevant code path,
> where eager split of folio can happen if the folio is already on deferred
> list during a folio migration.
>
> Here the issue is NUMA path (migrate_misplaced_folio()) may start to
> encounter such folio split now even with MR_NUMA_MISPLACED hint applied.
> Then when migrate_pages() didn't migrate all the folios, it's possible the
> split small folios be put onto the list instead of the original folio.
> Then putting back only the head page won't be enough.
>
> Fix it by putting back all the folios on the list.
>
> [1] https://lore.kernel.org/all/46c948b4-4dd8-6e03-4c7b-ce4e81cfa536@google.com/
>
> Cc: Zi Yan <ziy@...dia.com>
> Cc: Yang Shi <shy828301@...il.com>
> Cc: Hugh Dickins <hughd@...gle.com>
> Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Cc: Huang Ying <ying.huang@...el.com>
> Cc: David Hildenbrand <david@...hat.com>
> Fixes: 7262f208ca68 ("mm/migrate: split source folio if it is on deferred split list")
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
>
> Don't need to copy stable if this can still hit 6.10..  Only smoke tested.
> ---
>  mm/migrate.c | 10 ++--------
>  1 file changed, 2 insertions(+), 8 deletions(-)

LGTM. Thanks. Reviewed-by: Zi Yan <ziy@...dia.com>


-- 
Best Regards,
Yan, Zi


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