Re: [PATCH v2 4/8] mm/compaction: correct comment of fast_find_migrateblock in isolate_migratepages

[Baolin Wang]

On 8/2/2023 5:37 PM, Kemeng Shi wrote:
> After 90ed667c03fe5 ("Revert "Revert "mm/compaction: fix set skip in
> fast_find_migrateblock"""), we remove skip set in fast_find_migrateblock.
> Correct comment that fast_find_block is used to avoid isolation_suitable
> check for pageblock returned from fast_find_migrateblock because
> fast_find_migrateblock will mark found pageblock skipped.
> Instead, comment that fast_find_block is used to avoid a redundant check
> of fast found pageblock which is already checked skip flag inside
> fast_find_migrateblock.
>
> Signed-off-by: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
> ---
>   mm/compaction.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 984c17a5c8fd..5c9dc4049e8e 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1966,8 +1966,8 @@ static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
>   		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
> +	 * fast_find_migrateblock will ignore pageblock skipped, so to avoid

These seem confusing to me, since the fast_find_migrateblock() did not 
ignore the skip flag checking. So how about below words?

"fast_find_migrateblock() has already ensured the pageblock is not set 
with a skipped flag, so to avoid the isolation_suitable check below 
again ..."

> +	 * the isolation_suitable check below again, check whether the fast
>   	 * search was successful.
>   	 */
>   	fast_find_block = low_pfn != cc->migrate_pfn && !cc->fast_search_fail;