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Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.14.0 Subject: Re: [PATCH 4/9] mm/compaction: simplify pfn iteration in isolate_freepages_range To: Kemeng Shi , linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, mgorman@techsingularity.net, david@redhat.com References: <20230805110711.2975149-1-shikemeng@huaweicloud.com> <20230805110711.2975149-5-shikemeng@huaweicloud.com> <43b726c1-3ea6-9acc-d4e4-c7deabcf7ecd@huaweicloud.com> From: Baolin Wang In-Reply-To: <43b726c1-3ea6-9acc-d4e4-c7deabcf7ecd@huaweicloud.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Stat-Signature: tu9opttnyassmn5htku5fi9o6zegngap X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 24AF3180012 X-HE-Tag: 1692094082-125182 X-HE-Meta: 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 I3DEJ8t6 MvAzlKcHFC/m0oUPn2z4xJ+QqVOkndVwPPITrf6wAlkgODpmxlus0mEsCBaJisd7aWg+jkHQ7NcG98GG6dtPXNGZSsDHmxsTFVWeYHGswLM/4zhZ3JnDlFnveRFcRsFJHtjgWyFKYxXCJr3NOdeEGmfmqawMnb2prSxaQIBp2nsKaimb7HqTEQ3Raiw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000002, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 8/15/2023 5:32 PM, Kemeng Shi wrote: > > > on 8/15/2023 4:38 PM, Baolin Wang wrote: >> >> >> On 8/5/2023 7:07 PM, Kemeng Shi wrote: >>> We call isolate_freepages_block in strict mode, continuous pages in >>> pageblock will be isolated if isolate_freepages_block successed. >>> Then pfn + isolated will point to start of next pageblock to scan >>> no matter how many pageblocks are isolated in isolate_freepages_block. >>> Use pfn + isolated as start of next pageblock to scan to simplify the >>> iteration. >> >> IIUC, the isolate_freepages_block() can isolate high-order free pages, which means the pfn + isolated can be larger than the block_end_pfn. So in your patch, the 'block_start_pfn' and 'block_end_pfn' can be in different pageblocks, that will break pageblock_pfn_to_page(). >> > In for update statement, we always update block_start_pfn to pfn and I mean, you changed to: 1) pfn += isolated; 2) block_start_pfn = pfn; 3) block_end_pfn = pfn + pageblock_nr_pages; But in 1) pfn + isolated can go outside of the currnet pageblock if isolating a high-order page, for example, located in the middle of the next pageblock. So that the block_start_pfn can point to the middle of the next pageblock, not the start position. Meanwhile after 3), the block_end_pfn can point another pageblock. Or I missed something else? > update block_end_pfn to pfn + pageblock_nr_pages. So they should point > to the same pageblock. I guess you missed the change to update of > block_end_pfn. :) >>> >>> Signed-off-by: Kemeng Shi >>> --- >>>   mm/compaction.c | 14 ++------------ >>>   1 file changed, 2 insertions(+), 12 deletions(-) >>> >>> diff --git a/mm/compaction.c b/mm/compaction.c >>> index 684f6e6cd8bc..8d7d38073d30 100644 >>> --- a/mm/compaction.c >>> +++ b/mm/compaction.c >>> @@ -733,21 +733,11 @@ isolate_freepages_range(struct compact_control *cc, >>>       block_end_pfn = pageblock_end_pfn(pfn); >>>         for (; pfn < end_pfn; pfn += isolated, >>> -                block_start_pfn = block_end_pfn, >>> -                block_end_pfn += pageblock_nr_pages) { >>> +                block_start_pfn = pfn, >>> +                block_end_pfn = pfn + pageblock_nr_pages) { >>>           /* Protect pfn from changing by isolate_freepages_block */ >>>           unsigned long isolate_start_pfn = pfn; >>>   -        /* >>> -         * pfn could pass the block_end_pfn if isolated freepage >>> -         * is more than pageblock order. In this case, we adjust >>> -         * scanning range to right one. >>> -         */ >>> -        if (pfn >= block_end_pfn) { >>> -            block_start_pfn = pageblock_start_pfn(pfn); >>> -            block_end_pfn = pageblock_end_pfn(pfn); >>> -        } >>> - >>>           block_end_pfn = min(block_end_pfn, end_pfn); >>>             if (!pageblock_pfn_to_page(block_start_pfn, >>