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Subject: Re: [PATCH] mm/compaction: fix set skip in fast_find_migrateblock
To:     Zhou Chuyi <zhouchuyi@bytedance.com>, <linux-mm@kvack.org>
References: <20220711123213.66068-1-zhouchuyi@bytedance.com>
CC:     Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
From:   Miaohe Lin <linmiaohe@huawei.com>
Message-ID: <8af11329-93d4-3bbd-fe4c-343663c00a1b@huawei.com>
Date:   Tue, 12 Jul 2022 10:26:47 +0800
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On 2022/7/11 20:32, Zhou Chuyi wrote:
> From: zhouchuyi <zhouchuyi@bytedance.com>
> 
> When we successfully find a pageblock in fast_find_migrateblock(), the block will be set skip-flag through set_pageblock_skip(). However, when entering isolate_migratepages_block(), the whole pageblock will be skipped due to the branch 'if (!valid_page && IS_ALIGNED(low_pfn, pageblock_nr_pages))'. Eventually we will goto isolate_abort and isolate nothing.
> Signed-off-by: zhouchuyi <zhouchuyi@bytedance.com>

It seems we should tweak the commit log to satisfy the checkpatch.pl first.

> ---
>  mm/compaction.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 1f89b969c..a1a2b50c8 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1852,7 +1852,6 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc)
>  					pfn = cc->zone->zone_start_pfn;
>  				cc->fast_search_fail = 0;
>  				found_block = true;
> -				set_pageblock_skip(freepage);

This looks like a real problem. Should we add a Fixes tag here? What's the runtime effect of it?

Thanks for your patch!

>  				break;
>  			}
>  		}
>