Messages in this thread | | | Date | Tue, 1 Aug 2023 11:34:57 +0800 | Subject | Re: [PATCH 4/8] mm/compaction: remove stale fast_find_block flag in isolate_migratepages | From | Baolin Wang <> |
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On 8/1/2023 11:24 AM, Kemeng Shi wrote: > > > on 8/1/2023 10:42 AM, Baolin Wang wrote: >> >> >> 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? >> >> > Actually, found pageblock could be set skip as: > 1. other compactor could mark this pageblock as skip after zone lock is realeased > in fast_find_migrateblock.
Yes, but your patch also can not close this race window, that means it can also be set skip flag after the isolation_suitable() validation by other compactors.
> 2. fast_find_migrateblock may uses pfn from reinit_migrate_pfn which is previously found > and sacnned. It could be fully sacnned and marked skip after it's first return from
Right, but now the 'fast_find_block' is false, and we will call isolation_suitable() to validate the skip flag.
> fast_find_migrateblock and it should be skipped. > Thanks!
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