linux-kernel - Re: [PATCH v2] mm:vmscan: shrink skip folio mapped by an exiting task

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Date: Fri, 2 Feb 2024 01:22:51 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Zhiguo Jiang <justinjiang@...o.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 opensource.kernel@...o.com
Subject: Re: [PATCH v2] mm:vmscan: shrink skip folio mapped by an exiting
 task

On Wed, 31 Jan 2024 21:12:44 +0800 Zhiguo Jiang <justinjiang@...o.com> wrote:

> --- 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;
> +	}

The code comment explains what the code does.  This is, as usual,
pretty obvious from reading the code!

A better comment is one which explains *why* the code is doing what it
does.