linux-kernel - Re: [PATCH] mm: shrink skip folio mapped by an exiting task

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Message-ID: <9381d6e6-14f5-4499-9d7a-ed28aa16a3d1@redhat.com>
Date: Tue, 2 Jul 2024 15:26:08 +0200
From: David Hildenbrand <david@...hat.com>
To: Zhiguo Jiang <justinjiang@...o.com>,
 Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Cc: opensource.kernel@...o.com
Subject: Re: [PATCH] mm: shrink skip folio mapped by an exiting task

On 21.02.24 12:49, Zhiguo Jiang wrote:
> If an anon folio reclaimed by shrink_inactive_list is mapped by an
> exiting task, this anon folio will be firstly swaped-out into
> swapspace in shrink flow and then this swap folio is freed in task
> exit flow. But if this folio mapped by an exiting task can skip
> shrink and be freed directly in task exiting flow, which will save
> swap-out time and alleviate the load of the tasks exiting process.
> The file folio is also similar.
> 
> And when system is low memory, it more likely to occur, because more
> backend applidatuions will be killed.
> 
> This patch can alleviate the load of the tasks exiting process.
> 
> Signed-off-by: Zhiguo Jiang <justinjiang@...o.com>
> ---
>   mm/rmap.c | 7 +++++++
>   1 file changed, 7 insertions(+)
>   mode change 100644 => 100755 mm/rmap.c
> 
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 3746a5531018..146e5f4ec069
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -840,6 +840,13 @@ static bool folio_referenced_one(struct folio *folio,
>   	int referenced = 0;
>   	unsigned long start = address, ptes = 0;
>   
> +	/* Skip this folio if it's mapped by an exiting task */
> +	if (unlikely(!atomic_read(&vma->vm_mm->mm_users)) ||
> +		unlikely(test_bit(MMF_OOM_SKIP, &vma->vm_mm->flags))) {
> +		pra->referenced = -1;
> +		return false;
> +	}
> +
>   	while (page_vma_mapped_walk(&pvmw)) {
>   		address = pvmw.address;
>   

... but what if it is shared among multiple processes and only one of 
them is exiting?

-- 
Cheers,

David / dhildenb