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[114.38.149.183]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2e97e83498csm30202765ad.35.2026.10.18.11.26.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 18 Oct 2026 11:26:58 -0700 (PDT) From: Yuan-Hao Hsu To: Rik van Riel Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, Andrew Morton , David Hildenbrand , Jason Gunthorpe , John Hubbard , Peter Xu , Suren Baghdasaryan , linux-mm@kvack.org Subject: Re: [RFC PATCH v3 8/8] mm/gup: batch contiguous same-folio PTEs into one refcount grab Date: Mon, 19 Oct 2026 02:26:52 +0800 Message-ID: <20261018182652.691-1-aa9736195201@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260811025157.1632867-9-riel@surriel.com> References: <20260811025157.1632867-1-riel@surriel.com> <20260811025157.1632867-9-riel@surriel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 91826A0008 X-Stat-Signature: c8dz8trfs9czqr89mtq8ucbmyjmghggb X-Rspam-User: X-HE-Tag: 1792348021-540947 X-HE-Meta: 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 p6OLd/Rz XRcuowJyZrnrbeSWnmEnlniE+8AlvytYQ/e0TAc5Z1Zl9bGvlQft7Y1xFWf0nyISmPcf/DR78TC/Ubu0nAl0UGz8247vF8/1QUK1iWTtEjSc/WqsUjTxyW0Ka2AaChXOc0kCFylPljVub1kCptJp7fjHKGeRiC07pwa/HbL2i1jICH5ilmnjg7XfpqvxzmdGYq11MnCIB5//YHltWEJyyz7r5HGD8/NC1Ca1FmVXlMrP3lfqzVlGNPPS32r4z0uJdCNHQGrXRFDsBNsooYt4FqRBI5JxRbfRJr34wOELQsicluTxEu6oOQN9BXGryc0UvBCr66cZXE5+QcSvrY+iiZhcpzdbdXvlHKi11Ma5GQ8eRmEsNFqmI8OGB/1Cs5K8IQ/T+zDlTyY8Jwyo= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 10 Aug 2026 22:51:57 -0400, Rik van Riel wrote: > Add follow_pte_batch() and give follow_page_pte_commit() a run length. > Each run starts with a full per-PTE resolve, then follow_pte_batch() > finds how many more PTEs extend it with a pte_same() scan rather than a > re-derivation of each page, and the run is committed with one refcount > grab. Runs stop at folio boundaries, so plain base pages are unaffected. One side effect worth a sentence in the changelog: with FOLL_TOUCH, folio_mark_accessed() now runs once per run instead of once per page. On the classic LRU the first call only sets PG_referenced and the second one activates the folio, so the old per-page loop activated a PTE-mapped large folio from its second page on, and a run now leaves it referenced but inactive. Measured with one get_user_pages() call over 2 MB of freshly faulted 64 kB folios (kprobe on folio_mark_accessed(), flags from /proc/kpageflags): before after folio_mark_accessed 512 per call 32 per call after 1st call 32 folios active 32 referenced, 0 active after 2nd call 32 active 32 active That matches what the other two paths already do (follow_huge_pmd() only calls touch_pmd(), GUP-fast only calls folio_set_referenced()), so it looks like the right outcome. It is still a visible change in aging for anything that reaches these folios through get_user_pages() rather than the fast path. Yuan-Hao Hsu