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Date: Mon, 11 Nov 2024 16:22:48 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Qiang Liu <liuq131@chinatelecom.cn>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mel Gorman
 <mgorman@techsingularity.net>, Laura Abbott <labbott@redhat.com>
Subject: Re: [PATCH] mm/compaction: fix the total_isolated in strict mode
Message-Id: <20241111162248.7af77e56c1ff4017d1ed4106@linux-foundation.org>
In-Reply-To: <20241102201621.95291-1-liuq131@chinatelecom.cn>
References: <20241102201621.95291-1-liuq131@chinatelecom.cn>
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On Sat,  2 Nov 2024 20:16:21 +0000 Qiang Liu <liuq131@chinatelecom.cn> wrote:

> If the last cycle reads bogus compound_order() and blockpfn > end_pfn occurs,
> it is possible that total_isolated will be less than nr_scanned. In this case,
> strict mode should return 0, but the “if (strict && blockpfn < end_pfn)”
> statement cannot recognize this situation
> 
> ...
>
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -699,7 +699,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
>  	 * pages requested were isolated. If there were any failures, 0 is
>  	 * returned and CMA will fail.
>  	 */
> -	if (strict && blockpfn < end_pfn)
> +	if (strict && (blockpfn < end_pfn || total_isolated != nr_scanned))
>  		total_isolated = 0;
>  
>  	cc->total_free_scanned += nr_scanned;

That's really old code.  What userspace-visible effects might this
have?  Is this from code inspection, or was some misbehaviour observed?

Thanks.