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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> <6921ae7e-0c30-0934-168c-9480ca30108f@huaweicloud.com> From: Baolin Wang In-Reply-To: <6921ae7e-0c30-0934-168c-9480ca30108f@huaweicloud.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: F3F3440036 X-Stat-Signature: 95hek44rrebaoyafpkcdsbt7eedk5gfj X-HE-Tag: 1690876850-605114 X-HE-Meta: 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 jsxNpcdT CF0buj1MmgV4c1R7py6cVgwK37MLubBUoS5jXwXfBxUutF0UHW8GBk1r2g6GBIkURYCgu1Not5bbQ+nY3znYHDQyPx1lKW5Z+nvATzFc/lGgXAWky7ArEXo4uOoT5jduqEXowNbMDzQ4VqjU= 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 2:08 PM, Kemeng Shi wrote: > > > on 8/1/2023 11:53 AM, Baolin Wang wrote: >> >> >> 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. >> > Right, I mixed up the unit. >> 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. >> > Sure, then we should assign block_start_pfn with following change. Is this good to you? > - block_start_pfn = max(pageblock_start_pfn(next_pfn), > + block_start_pfn = max(pageblock_end_pfn(next_pfn), > low_pfn); The last pfn of a section is already section aligned, so I think no need to call pageblock_end_pfn(), just like your original change is okay to me. block_start_pfn = max(next_pfn, low_pfn);