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Wed, 09 Apr 2025 17:49:52 +0800 Message-ID: <0e294c56-d924-4d40-aa24-584235e8c923@linux.alibaba.com> Date: Wed, 9 Apr 2025 17:49:52 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: huge_memory: add folio_mark_accessed() when zapping file THP To: David Hildenbrand , akpm@linux-foundation.org Cc: willy@infradead.org, hannes@cmpxchg.org, 21cnbao@gmail.com, ryan.roberts@arm.com, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <39176ab9-33d5-4919-b368-2fd2467f08fe@redhat.com> From: Baolin Wang In-Reply-To: <39176ab9-33d5-4919-b368-2fd2467f08fe@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: DE5CA140005 X-Stat-Signature: d674t5oy9uohb86bfagocyfgs45zj9mw X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1744192198-226132 X-HE-Meta: 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 GHoBTrRs q0dZLe1qtAh5E+Nz2sboMveWmjqcMcn+eT7rVdj86nxmFyVyEG/G24MhyWN3jh9BCjuHDEGIYC18y6sUJmoes0jaLvotMk8H+6Q0iEmYKLxAsebMX7KPfhCWHgwuJRkfEqUhPXFtdtIuJjRD1+/jyODMZxhj9EapTIhY1Dn3xecpoy8XKGzpiOSxq83AlukzfV5aZ8kKNmcDjOK1ZQA4Cl02ZrZLXtv1xYHpcRdHkZR1ava1baXI1D3okPDRNyMbWjYCvIagAODY+gvo5df8OUjI/1Za5CVp58WgR1NsTGOPeS6ZOwb97qLKC0Q6XvuXUeTeqBkIPATvzGoygzvSbv8FFNmc0T6UKfzV54PT68/46atYQODzrD6dyw3NnjLmrS724Zzqz1k8n7AKZtEpBIIwZo2zJBYy761gUxUr+FDojpcRA000HGI01SCsyal727X3D 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: List-Subscribe: List-Unsubscribe: On 2025/4/9 17:46, David Hildenbrand wrote: > On 09.04.25 11:38, Baolin Wang wrote: >> When investigating performance issues during file folio unmap, I >> noticed some >> behavioral differences in handling non-PMD-sized folios and PMD-sized >> folios. >> For non-PMD-sized file folios, it will call folio_mark_accessed() to >> mark the >> folio as having seen activity, but this is not done for PMD-sized folios. >> >> This might not cause obvious issues, but a potential problem could be >> that, >> it might lead to reclaim hot file folios under memory pressure, as quoted >> from Johannes: >> >> " >> Sometimes file contents are only accessed through relatively short-lived >> mappings. But they can nevertheless be accessed a lot and be hot. It's >> important to not lose that information on unmap, and end up kicking out a >> frequently used cache page. >> " >> >> Therefore, we should also add folio_mark_accessed() for PMD-sized file >> folios when unmapping. >> >> Signed-off-by: Baolin Wang >> Acked-by: Johannes Weiner >> Acked-by: Zi Yan >> --- >> Changes from RFC: >>   - Update the commit message, per Johannes. >>   - Collect Acked tags from Johannes and Zi. Thanks. >> --- >>   mm/huge_memory.c | 4 ++++ >>   1 file changed, 4 insertions(+) >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 2a47682d1ab7..955781b4e946 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -2260,6 +2260,10 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct >> vm_area_struct *vma, >>                   zap_deposited_table(tlb->mm, pmd); >>               add_mm_counter(tlb->mm, mm_counter_file(folio), >>                          -HPAGE_PMD_NR); >> + >> +            if (flush_needed && pmd_young(orig_pmd) && >> +                likely(vma_has_recency(vma))) >> +                folio_mark_accessed(folio); > > So the flush_needed check is really just a pmd_present() check. (the > latter would be clearer, but I don't mind) Yes, we've already checked pmd_present() before, so I assume the flush_needed check is cheaper:) > Acked-by: David Hildenbrand Thanks.