linux-kernel - Re: [PATCH] mm:vmscan: fix return negative unneed to detect VM

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Message-Id: <20231106104049.1ed5ba7976f0c0633fb729f5@linux-foundation.org>
Date:   Mon, 6 Nov 2023 10:40:49 -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] mm:vmscan: fix return negative unneed to detect VM_EXEC

On Wed, 25 Oct 2023 23:44:32 +0800 Zhiguo Jiang <justinjiang@...o.com> wrote:

> The reason that folio_referenced() returns negative is because
> rwc.contended is 1, vm_flags is 0 at this time and so there is
> no need to detect VM_EXEC. And only when referenced > 0, pra->vm_flags
> will be filled with vma->vm_flags in folio_referenced_one().
> 
> ...
>
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2095,7 +2095,7 @@ static void shrink_active_list(unsigned long nr_to_scan,
>  
>  		/* Referenced or rmap lock contention: rotate */
>  		if (folio_referenced(folio, 0, sc->target_mem_cgroup,
> -				     &vm_flags) != 0) {
> +				     &vm_flags) > 0) {
>  			/*
>  			 * Identify referenced, file-backed active folios and
>  			 * give them one more trip around the active list. So

I suspect this email did not make it through the linux-mm server.  I
can't find it in my archive or at https://lore.kernel.org/linux-mm/.

So please resend?  Prior to doing so, please update the changelog to
describe the before- and after- userspace visible effects of the
change.

Thanks.