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[2003:d8:2f3c:2f00:8afc:23fe:3813:776c]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4538a3a6716sm11886905e9.11.2025.06.26.01.17.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 26 Jun 2025 01:17:14 -0700 (PDT) Message-ID: Date: Thu, 26 Jun 2025 10:17:13 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 , Barry Song <21cnbao@gmail.com> 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 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> <9bb1e917-891d-4e1b-915f-98cdd5fc578b@redhat.com> <42343413-7089-404e-8ce0-dd0025dca04c@linux.dev> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 26.06.25 03:17, Lance Yang wrote: > > > On 2025/6/26 05:03, Barry Song wrote: >> On Thu, Jun 26, 2025 at 12:25 AM David Hildenbrand wrote: >>> >>> On 25.06.25 14:20, Lance Yang wrote: >> [...] >>>> 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); >> >> Because we've already called folio_ref_sub(folio, nr_pages - 1); >> Looking back, it’s kind of ugly, huh. >> >> discard: >> if (unlikely(folio_test_hugetlb(folio))) { >> hugetlb_remove_rmap(folio); >> } else { >> folio_remove_rmap_ptes(folio, subpage, nr_pages, vma); >> folio_ref_sub(folio, nr_pages - 1); >> } >> >> I assume Lance will send a patch? If so, remember to remove this >> when switching to folio_put_refs(folio, nr_pages); > > Ah, got it. Thanks for pointing that out! Obviously I was hinting that the split refcount update can be merged into a single refcount update :) -- Cheers, David / dhildenb