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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> <3729c50f-6f8e-2548-8932-f39045402299@linux.alibaba.com> <3574ed6e-34c8-47a1-8218-9e4cf1327184@huaweicloud.com> From: Baolin Wang In-Reply-To: <3574ed6e-34c8-47a1-8218-9e4cf1327184@huaweicloud.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: EAEA64000B X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: c4cihjgm5xe5g6p3zrpkeft7befr9c6e X-HE-Tag: 1692446337-706679 X-HE-Meta: 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 r7DLNohB edYM1/+N3RPBPMKPw+20A1bzlZs1xCQxl1vdUB/+vOtfqZaoIa6PJic8QHzW3gQNM999FMCtnDLhaZ69zbXhIQQoQFm7skOU3iWG+YXl/oM0ZYTiYHFSBnGhaX1DzQAKtndd0uMuf+tCghBT02kraxHK2WJhoFNGHdy5xRHwSvlOpZhHdpBTpqZPxoLLC/SGMhpBO X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 8/15/2023 6:37 PM, Kemeng Shi wrote: > > > on 8/15/2023 6:07 PM, Baolin Wang wrote: >> >> >> 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? >> > Ah, I miss to explain this in changelog. > In case we could we have buddy page with order higher than pageblock: > 1. page in buddy page is aligned with it's order > 2. order of page is higher than pageblock order > Then page is aligned with pageblock order. So pfn of page and isolated pages > count are both aligned pageblock order. So pfn + isolated is pageblock order > aligned. That's not what I mean. pfn + isolated is not always pageblock-aligned, since the isolate_freepages_block() can isolated high-order free pages (for example: order-1, order-2 ...). Suppose the pageblock size is 2M, when isolating a pageblock (suppose the pfn range is 0 - 511 to make the arithmetic easy) by isolate_freepages_block(), and suppose pfn 0 to pfn 510 are all order-0 page, but pfn 511 is order-1 page, so you will isolate 513 pages from this pageblock, which will make 'pfn + isolated' not pageblock aligned. >>> 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, >>>> >>