Re: [PATCH v2 2/8] mm/compaction: correct last_migrated_pfn update in compact_zone

[Baolin Wang]

On 8/2/2023 5:37 PM, Kemeng Shi wrote:
> We record start pfn of last isolated page block with last_migrated_pfn. And
> then:
> 1. We check if we mark the page block skip for exclusive access in
> isolate_migratepages_block by test if next migrate pfn is still in last
> isolated page block. If so, we will set finish_pageblock to do the rescan.
> 2. We check if a full cc->order block is scanned by test if last scan range
> passes the cc->order block boundary. If so, we flush the pages were freed.
>
> We treat cc->migrate_pfn before isolate_migratepages as the start pfn of
> last isolated page range. However, we always align migrate_pfn to page block
> or move to another page block in fast_find_migrateblock or in linearly scan
> forward in isolate_migratepages before do page isolation in
> isolate_migratepages_block.
>
> Update last_migrated_pfn with pageblock_start_pfn(cc->migrate_pfn - 1)
> after scan to correctly set start pfn of last isolated page range. To
> avoid that:
> 1. Miss a rescan with finish_pageblock set as last_migrate_pfn does not
> point to right pageblock and the migrate will not be in pageblock of
> last_migrate_pfn as it should be.
> 2. Wrongly issue flush by test cc->order block boundary with wrong
> last_migrate_pfn.
>
> Signed-off-by: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>

LGTM.
Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>

> ---
>   mm/compaction.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index a8cea916df9d..ec3a96b7afce 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -2487,7 +2487,8 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
>   			goto check_drain;
>   		case ISOLATE_SUCCESS:
>   			update_cached = false;
> -			last_migrated_pfn = iteration_start_pfn;
> +			last_migrated_pfn = max(cc->zone->zone_start_pfn,
> +				pageblock_start_pfn(cc->migrate_pfn - 1));
>   		}
>   
>   		err = migrate_pages(&cc->migratepages, compaction_alloc,