linux-kernel - Re: [PATCH v2 3/3] mm: memory-hotplug: check folio ref count first in do_migrate

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Message-ID: <7ff8de59-f91e-4d39-8b6a-2f135b2a2397@redhat.com>
Date: Mon, 20 Jan 2025 09:01:41 +0100
From: David Hildenbrand <david@...hat.com>
To: Wupeng Ma <mawupeng1@...wei.com>, akpm@...ux-foundation.org,
 osalvador@...e.de, nao.horiguchi@...il.com, linmiaohe@...wei.com,
 mhocko@...e.com
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] mm: memory-hotplug: check folio ref count first in
 do_migrate_rang

On 16.01.25 07:16, Wupeng Ma wrote:
> From: Ma Wupeng <mawupeng1@...wei.com>
> 
> If a folio has an increased reference count, folio_try_get() will acquire
> it, perform necessary operations, and then release it. In the case of a
> poisoned folio without an elevated reference count (which is unlikely for
> memory-failure), folio_try_get() will simply bypass it.
> 
> Therefore, relocate the folio_try_get() function, responsible for checking
> and acquiring this reference count at first.
> 
> Signed-off-by: Ma Wupeng <mawupeng1@...wei.com>
> ---
>   mm/memory_hotplug.c | 14 ++++----------
>   1 file changed, 4 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 2815bd4ea483..3fb75ee185c6 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1786,6 +1786,9 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
>   		page = pfn_to_page(pfn);
>   		folio = page_folio(page);
>   
> +		if (!folio_try_get(folio))
> +			continue;
> +

I would only move it in front of the folio_test_hwpoison() check for 
now. Note that with this patch as is the comment below would be wrong

>   		/*
>   		 * No reference or lock is held on the folio, so it might

^

I would move this patch before the current #2, so the folio_lock() looks 
less weird.

-- 
Cheers,

David / dhildenb