Re: [PATCH 4/8] mm/compaction: remove stale fast_find_block flag in isolate_migratepages

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 7/29/2023 1:10 AM, Kemeng Shi wrote:
> In old code, we set skip to found page block in fast_find_migrateblock. So
> we use fast_find_block to avoid skip found page block from
> fast_find_migrateblock.
> In 90ed667c03fe5 ("Revert "Revert "mm/compaction: fix set skip in
> fast_find_migrateblock"""), we remove skip set in fast_find_migrateblock,
> then fast_find_block is useless.
> 
> Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
> ---
>   mm/compaction.c | 12 +-----------
>   1 file changed, 1 insertion(+), 11 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index ad535f880c70..09c36251c613 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1949,7 +1949,6 @@ static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
>   	const isolate_mode_t isolate_mode =
>   		(sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
>   		(cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);
> -	bool fast_find_block;
>   
>   	/*
>   	 * Start at where we last stopped, or beginning of the zone as
> @@ -1961,13 +1960,6 @@ static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
>   	if (block_start_pfn < cc->zone->zone_start_pfn)
>   		block_start_pfn = cc->zone->zone_start_pfn;
>   
> -	/*
> -	 * fast_find_migrateblock marks a pageblock skipped so to avoid
> -	 * the isolation_suitable check below, check whether the fast
> -	 * search was successful.
> -	 */
> -	fast_find_block = low_pfn != cc->migrate_pfn && !cc->fast_search_fail;
> -
>   	/* Only scan within a pageblock boundary */
>   	block_end_pfn = pageblock_end_pfn(low_pfn);
>   
> @@ -1976,7 +1968,6 @@ static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
>   	 * Do not cross the free scanner.
>   	 */
>   	for (; block_end_pfn <= cc->free_pfn;
> -			fast_find_block = false,
>   			cc->migrate_pfn = low_pfn = block_end_pfn,
>   			block_start_pfn = block_end_pfn,
>   			block_end_pfn += pageblock_nr_pages) {
> @@ -2007,8 +1998,7 @@ static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
>   		 * before making it "skip" so other compaction instances do
>   		 * not scan the same block.
>   		 */
> -		if (pageblock_aligned(low_pfn) &&
> -		    !fast_find_block && !isolation_suitable(cc, page))
> +		if (pageblock_aligned(low_pfn) && !isolation_suitable(cc, page))

I do not think so. If the pageblock is found by 
fast_find_migrateblock(), that means it definitely has not been set the 
skip flag, so there is not need to call isolation_suitable() if 
fast_find_block is true, right?