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Shutemov" , Yin Fengwei , "David Hildenbrand" , Yu Zhao , "Catalin Marinas" , Will Deacon , "Anshuman Khandual" , Yang Shi , , , Subject: Re: [PATCH v2 2/5] mm: Allow deferred splitting of arbitrary large anon folios References: <20230703135330.1865927-1-ryan.roberts@arm.com> <20230703135330.1865927-3-ryan.roberts@arm.com> <877crcgmj1.fsf@yhuang6-desk2.ccr.corp.intel.com> <6379dd13-551e-3c73-422a-56ce40b27deb@arm.com> Date: Mon, 10 Jul 2023 13:37:24 +0800 In-Reply-To: <6379dd13-551e-3c73-422a-56ce40b27deb@arm.com> (Ryan Roberts's message of "Fri, 7 Jul 2023 10:42:26 +0100") Message-ID: <87ttucfht7.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Stat-Signature: ge68mhcj5b8mp9d7qcgitxkoi593jboh X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 2D37AC0007 X-Rspam-User: X-HE-Tag: 1688967556-285154 X-HE-Meta: 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 qgULLfzH q5BEuT++oTZSZPumfRXP/FXuwZ7xvOjPVAkzR8LcAIIYF91I+gCNb8CkKMyUWk5RgaW6Pb1GeF41RnEeaMrF825kj9VeE2+AwguMPvlcjskDG4tMre7Qgakj4G4Tc+auNirLXxicdP/lDeu3bKdyax9wfVNB3gyZeCp5ucbQvVciTyYM0keoNl0coihafNHH514uek/wtsQV3jkJULnDiOgUGfhzUcclHDR9IOfWhfKH6a8CSpOX6RiLL8q8dPvoXq+HtuebaMtomAHB/U3C2esowhSmTZklM9csM14Dvc7jQKmUUY/kaW55Tpc7riiIqGncDhSSXoaIdNOVwsmJgqQSdWz3QWEYCwQvVNfTotf9Z0VTsl+QLDaoUS3YMMBZbOKt1xgwRRXiOLc9K/n3OAtDgwA== 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: Ryan Roberts writes: > Somehow I managed to reply only to the linux-arm-kernel list on first attempt so > resending: > > On 07/07/2023 09:21, Huang, Ying wrote: >> Ryan Roberts writes: >> >>> With the introduction of large folios for anonymous memory, we would >>> like to be able to split them when they have unmapped subpages, in order >>> to free those unused pages under memory pressure. So remove the >>> artificial requirement that the large folio needed to be at least >>> PMD-sized. >>> >>> Signed-off-by: Ryan Roberts >>> Reviewed-by: Yu Zhao >>> Reviewed-by: Yin Fengwei >>> --- >>> mm/rmap.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/mm/rmap.c b/mm/rmap.c >>> index 82ef5ba363d1..bbcb2308a1c5 100644 >>> --- a/mm/rmap.c >>> +++ b/mm/rmap.c >>> @@ -1474,7 +1474,7 @@ void page_remove_rmap(struct page *page, struct vm_area_struct *vma, >>> * page of the folio is unmapped and at least one page >>> * is still mapped. >>> */ >>> - if (folio_test_pmd_mappable(folio) && folio_test_anon(folio)) >>> + if (folio_test_large(folio) && folio_test_anon(folio)) >>> if (!compound || nr < nr_pmdmapped) >>> deferred_split_folio(folio); >>> } >> >> One possible issue is that even for large folios mapped only in one >> process, in zap_pte_range(), we will always call deferred_split_folio() >> unnecessarily before freeing a large folio. > > Hi Huang, thanks for reviewing! > > I have a patch that solves this problem by determining a range of ptes covered > by a single folio and doing a "batch zap". This prevents the need to add the > folio to the deferred split queue, only to remove it again shortly afterwards. > This reduces lock contention and I can measure a performance improvement for the > kernel compilation benchmark. See [1]. > > However, I decided to remove it from this patch set on Yu Zhao's advice. We are > aiming for the minimal patch set to start with and wanted to focus people on > that. I intend to submit it separately later on. > > [1] https://lore.kernel.org/linux-mm/20230626171430.3167004-8-ryan.roberts@arm.com/ Thanks for your information! "batch zap" can solve the problem. And, I agree with Matthew's comments to fix the large folios interaction issues before merging the patches to allocate large folios as in the following email. https://lore.kernel.org/linux-mm/ZKVdUDuwNWDUCWc5@casper.infradead.org/ If so, we don't need to introduce the above problem or a large patchset. Best Regards, Huang, Ying