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c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1690861714; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=dh5WOUdxYqKJy6Y1VuFT2ctaH24/U2Rz2C6SRzkQklI=; b=b8CkgJEa7pA+WxlfIqbzwOyfL2eQE6D269cVrKga0YGbujy/hhsUSgsuLjUW8t4JoqO3gd zzwMOshPsoV2QQDAe4QStPVZGqIR7ARNAvFqY9BStQNK7FHHIWzBQebG4cH70rRFK02SqK ZUA5oVCFE+FdosB4bb/UpjCzhBU6A9c= Received: from mail02.huawei.com (unknown [172.30.67.143]) by dggsgout12.his.huawei.com (SkyGuard) with ESMTP id 4RFLgF1L8bz4f3jHj for ; Tue, 1 Aug 2023 11:48:25 +0800 (CST) Received: from [10.174.178.129] (unknown [10.174.178.129]) by APP4 (Coremail) with SMTP id gCh0CgBnHLCKgMhkN3IpPQ--.25762S2; Tue, 01 Aug 2023 11:48:27 +0800 (CST) Subject: Re: [PATCH 4/8] mm/compaction: remove stale fast_find_block flag in isolate_migratepages To: Baolin Wang , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, mgorman@techsingularity.net, willy@infradead.org, david@redhat.com References: <20230728171037.2219226-1-shikemeng@huaweicloud.com> <20230728171037.2219226-5-shikemeng@huaweicloud.com> From: Kemeng Shi Message-ID: Date: Tue, 1 Aug 2023 11:48:26 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; 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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. > > 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 comment that "fast_find_migrateblock marks a pageblock skipped ..." in next version. Thanks! >> fast_find_migrateblock and it should be skipped. >> Thanks! > -- Best wishes Kemeng Shi