linux-kernel - Re: [PATCH v2] mm/compaction: Rename 'start_pfn' to 'iteration_start_pfn' in compact

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Date:   Mon, 19 Oct 2020 11:40:07 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     yanfei.xu@...driver.com, akpm@...ux-foundation.org,
        david@...hat.com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm/compaction: Rename 'start_pfn' to
 'iteration_start_pfn' in compact_zone()

On 10/19/20 10:36 AM, yanfei.xu@...driver.com wrote:
> From: Yanfei Xu <yanfei.xu@...driver.com>
> 
> There are two 'start_pfn' declared in compact_zone() which have
> different meaning. Rename the second one to 'iteration_start_pfn'
> to prevent trace_mm_compaction_end() from tracing an undesirable
> value.

"to prevent confusion.", because trace_mm_compaction_end() has the
correct value even before the patch - the second start_pfn is out
of scope at that point.

Thanks

> BTW, remove an useless semicolon.
> 
> Acked-by: David Hildenbrand <david@...hat.com>
> Acked-by: Vlastimil Babka <vbabka@...e.cz>
> Signed-off-by: Yanfei Xu <yanfei.xu@...driver.com>
> ---
> v1->v2:
> Rename 'start_pfn' to 'iteration_start_pfn' and change commit messages.
> 
>   mm/compaction.c | 7 +++----
>   1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 176dcded298e..ccd27c739fd6 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -2272,7 +2272,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
>   
>   	while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) {
>   		int err;
> -		unsigned long start_pfn = cc->migrate_pfn;
> +		unsigned long iteration_start_pfn = cc->migrate_pfn;
>   
>   		/*
>   		 * Avoid multiple rescans which can happen if a page cannot be
> @@ -2284,7 +2284,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
>   		 */
>   		cc->rescan = false;
>   		if (pageblock_start_pfn(last_migrated_pfn) ==
> -		    pageblock_start_pfn(start_pfn)) {
> +		    pageblock_start_pfn(iteration_start_pfn)) {
>   			cc->rescan = true;
>   		}
>   
> @@ -2308,8 +2308,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
>   			goto check_drain;
>   		case ISOLATE_SUCCESS:
>   			update_cached = false;
> -			last_migrated_pfn = start_pfn;
> -			;
> +			last_migrated_pfn = iteration_start_pfn;
>   		}
>   
>   		err = migrate_pages(&cc->migratepages, compaction_alloc,
>