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[2003:d8:2f12:1b00:5d6b:db26:e2b7:12]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a6e80f294asm4571380f8f.58.2025.06.25.05.25.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 25 Jun 2025 05:25:26 -0700 (PDT) Message-ID: <9bb1e917-891d-4e1b-915f-98cdd5fc578b@redhat.com> Date: Wed, 25 Jun 2025 14:25:24 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 3/4] mm: Support batched unmap for lazyfree large folios during reclamation To: Lance Yang Cc: akpm@linux-foundation.org, baolin.wang@linux.alibaba.com, chrisl@kernel.org, kasong@tencent.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, lorenzo.stoakes@oracle.com, ryan.roberts@arm.com, v-songbaohua@oppo.com, x86@kernel.org, ying.huang@intel.com, zhengtangquan@oppo.com, Lance Yang , Barry Song <21cnbao@gmail.com> References: <2c19a6cf-0b42-477b-a672-ed8c1edd4267@redhat.com> <20250624162503.78957-1-ioworker0@gmail.com> <27d174e0-c209-4851-825a-0baeb56df86f@redhat.com> <938c4726-b93e-46df-bceb-65c7574714a6@linux.dev> <5ba95609-302b-456a-a863-2bd5df51baf2@redhat.com> <6179dd30-5351-4a79-b0d6-f0e85650a926@redhat.com> <5db6fb4c-079d-4237-80b3-637565457f39@redhat.com> <42f1d84f-2d17-43b7-8fa2-83322fcca44f@linux.dev> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 179C9120002 X-Stat-Signature: po1jie6z8n5bqgmx9x9shin63ec315yx X-HE-Tag: 1750854330-986273 X-HE-Meta: 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 yd6mvxyh EWYzwJQip7+aCCFVHhJW7zBuqg3I8grVEA8Xal5z56fiVOCDauatnzlxaY48d1t5425Gzbg0H15DlBhIWWSw3Pfq3+E3BXORI1dNDq5KmBwTI1YRMUA7a7PzuhB9iFQqfBho1H0gtGu5+U0CKsiGKyrrMgU72HbnoRab8gKVOz9dIZ1H79to6kgnMbfI9OIJ+FY01DiTEyEINes22zPdycrrJJXEDTChlhh0ySkX1CdM0NnMNroEFdqzz3z6WM6C8g5jCvxto5je0ATFLbF1ayNV5qGlQYwPuwWtlFr72tID9Z/K3gDsIsjOWrEIjr5C8y3emF0pJAKHKoHWKH4axG5jD8Rnl5tKDNZcGXqTXzyTxswLJ3gLcf1c6bA+kkVTBsVJO/9Eio3Oda8cv/MkZKFBt4bfYgbBiwVAfuLJqm/MeIIl2StDCFdRN9+R5syV//IhgDJHZl18EUjIDHQ0MNpABTEHJLYJWCc8z1SNz54LORZM= 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 25.06.25 14:20, Lance Yang wrote: > > > On 2025/6/25 20:09, David Hildenbrand wrote: >>> >>> Somehow, I feel we could combine your cleanup code—which handles a batch >>> size of "nr" between 1 and nr_pages—with the >>> "if (nr_pages == folio_nr_pages(folio)) goto walk_done" check. >> >> Yeah, that's what I was suggesting. It would have to be part of the >> cleanup I think. >> >> I'm still wondering if there is a case where >> >> if (nr_pages == folio_nr_pages(folio)) >>     goto walk_done; >> >> would be wrong when dealing with small folios. >> >>> In practice, this would let us skip almost all unnecessary checks, >>> except for a few rare corner cases. >>> >>> For those corner cases where "nr" truly falls between 1 and nr_pages, >>> we can just leave them as-is—performing the redundant check inside >>> page_vma_mapped_walk(). >> >> I mean, batching mapcount+refcount updates etc. is always a win. If we >> end up doing some unnecessary pte_none() checks, that might be >> suboptimal but mostly noise in contrast to the other stuff we will >> optimize out 🙂 >> >> Agreed that if we can easily avoid these pte_none() checks, we should do >> that. Optimizing that for "nr_pages == folio_nr_pages(folio)" makes sense. > > Hmm... I have a question about the reference counting here ... > > if (vma->vm_flags & VM_LOCKED) > mlock_drain_local(); > folio_put(folio); > /* We have already batched the entire folio */ > > Does anyone else still hold a reference to this folio after folio_put()? The caller of the unmap operation should better hold a reference :) Also, I am not sure why we don't perform a folio_put_refs(folio, nr_pages); ... :) -- Cheers, David / dhildenb