linux-kernel - Re: [PATCH] khugepaged: Reduce race probability between migration and khugepaged

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Message-ID: <5e5b726c-b14b-45fa-b444-0e2aa5c84de1@linux.alibaba.com>
Date: Mon, 30 Jun 2025 15:46:57 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Dev Jain <dev.jain@....com>, akpm@...ux-foundation.org, david@...hat.com
Cc: ziy@...dia.com, lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com,
 npache@...hat.com, ryan.roberts@....com, baohua@...nel.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] khugepaged: Reduce race probability between migration and
 khugepaged



On 2025/6/30 12:48, Dev Jain wrote:
> Suppose a folio is under migration, and khugepaged is also trying to
> collapse it. collapse_pte_mapped_thp() will retrieve the folio from the
> page cache via filemap_lock_folio(), thus taking a reference on the folio
> and sleeping on the folio lock, since the lock is held by the migration
> path. Migration will then fail in
> __folio_migrate_mapping -> folio_ref_freeze. Reduce the probability of
> such a race happening (leading to migration failure) by bailing out
> if we detect a PMD is marked with a migration entry.
> 
> This fixes the migration-shared-anon-thp testcase failure on Apple M3.
> 
> Note that, this is not a "fix" since it only reduces the chance of
> interference of khugepaged with migration, wherein both the kernel
> functionalities are deemed "best-effort".
> 
> Signed-off-by: Dev Jain <dev.jain@....com>
> ---

Looks reasonable to me.
Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>