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Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH 1/8] mm/compaction: avoid missing last page block in section after skip offline sections To: Kemeng Shi , 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> <20230728171037.2219226-2-shikemeng@huaweicloud.com> <6e76323f-a1cc-7d20-676e-4eccdbcf6b91@linux.alibaba.com> <9b207dbf-1652-4851-7c6e-16220d5f2f3b@huaweicloud.com> From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: C47B440009 X-Stat-Signature: 1g6hth33u7wkwqfck6jjnwfx8q955paa X-Rspam-User: X-HE-Tag: 1690862012-269614 X-HE-Meta: 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 bSBRCmDG XLAgGcz6n/et9It9+MtvPuV+2Lq9jfW/vwNPclDi7oFjnvBAD42OFDOY24EbBcHao1PX8wFzZsq/DpVBAfFk4yrhw2JgefU8GB2QWObt5pioJuWfgNckMWNiKLSOjTcN68h2FxpaH1POS8sc= 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 8/1/2023 10:36 AM, Kemeng Shi wrote: > > > on 8/1/2023 10:18 AM, Kemeng Shi wrote: >> >> >> on 7/31/2023 8:01 PM, Baolin Wang wrote: >>> >>> >>> On 7/29/2023 1:10 AM, Kemeng Shi wrote: >>>> skip_offline_sections_reverse will return the last pfn in found online >>>> section. Then we set block_start_pfn to start of page block which >>>> contains the last pfn in section. Then we continue, move one page >>>> block forward and ignore the last page block in the online section. >>>> Make block_start_pfn point to first page block after online section to fix >>>> this: >>>> 1. make skip_offline_sections_reverse return end pfn of online section, >>>> i.e. pfn of page block after online section. >>>> 2. assign block_start_pfn with next_pfn. >>>> >>>> Fixes: f63224525309 ("mm: compaction: skip the memory hole rapidly when isolating free pages") >>>> Signed-off-by: Kemeng Shi >>>> --- >>>>   mm/compaction.c | 5 ++--- >>>>   1 file changed, 2 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/mm/compaction.c b/mm/compaction.c >>>> index 9b7a0a69e19f..ce7841363b12 100644 >>>> --- a/mm/compaction.c >>>> +++ b/mm/compaction.c >>>> @@ -259,7 +259,7 @@ static unsigned long skip_offline_sections_reverse(unsigned long start_pfn) >>>>         while (start_nr-- > 0) { >>>>           if (online_section_nr(start_nr)) >>>> -            return section_nr_to_pfn(start_nr) + PAGES_PER_SECTION - 1; >>>> +            return section_nr_to_pfn(start_nr + 1); >>> >>> This is incorrect, you returned the start pfn of this section. >>> >>>>       } >>>>         return 0; >>>> @@ -1670,8 +1670,7 @@ static void isolate_freepages(struct compact_control *cc) >>>>                 next_pfn = skip_offline_sections_reverse(block_start_pfn); >>>>               if (next_pfn) >>>> -                block_start_pfn = max(pageblock_start_pfn(next_pfn), >>>> -                              low_pfn); >>>> +                block_start_pfn = max(next_pfn, low_pfn); >>> >>> 'block_start_pfn' should be pageblock aligned. If the 'next_pfn' is not pageblock-aligned (though this is not the common case), we should skip it. >>> >>> But if the 'next_pfn' is pageblock-aligned, yes, the commit f63224525309 still ignores the last pageblock, which is not right. So I think it should be: >>> block_start_pfn = pageblock_aligned(next_pfn) ? : pageblock_start_pfn(next_pfn); >>> block_start_pfn = max(block_start_pfn, low_pfn); >>> >> Hi Baolin, thanks for reply! As skip_offline_sections_reverse is based >> on skip_offline_sections. I make the assumption that section is pageblock >> aligned based on that we use section start from skip_offline_sections as >> block_start_fpn without align check. >> If section size is not pageblock aligned in real world, the pageblock aligned >> check should be added to skip_offline_sections and skip_offline_sections_reverse. >> If no one is against this, I will fix this in next version. THanks! >> > More information of aligment of section. For powerpc arch, we have SECTION_SIZE_BITS > with 24 while PAGE_SHIFT could be configured to 18. > Pageblock order is (18 + MAX_ORDER) which coule be 28 and is > SECTION_SZIE_BITS 24, The maximum pageblock order is MAX_ORDER. But after thinking more, I think return the start pfn or end pfn of a section is okay, and it should be aligned to a pageblock order IIUC. So I think your change is good: + block_start_pfn = max(next_pfn, low_pfn); But in skip_offline_sections_reverse(), we should still return the last pfn of the online section.