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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 >> --- >>   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. 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 fast_find_migrateblock and it should be skipped. Thanks! -- Best wishes Kemeng Shi