Messages in this thread | | | Date | Tue, 1 Aug 2023 16:15:27 +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 11:48 AM, Kemeng Shi wrote: > > > on 8/1/2023 11:34 AM, Baolin Wang wrote: >> >> >> 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. >> > Yes, I think it's still worth to remove a lot of fast_find_block relevant check and reduce > code complexity with one redundant isolation_suitable which may skip some block with luck. >>> 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. >> > Right, sorry for missing that. > > But it's ok to keep the fast_find_block if you insist and I will just correct the stale
Yes, I still prefer to keep the fast_find_block, since I did not see this patch can fix any real issue and might have a side effect for fast-find-pageblock(?).
> comment that "fast_find_migrateblock marks a pageblock skipped ..." in next version.
Sure, please do it.
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