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Received: from [2601:18c:8100:a0e0:2541:b86e:2586:d219] by shelob.surriel.com with esmtpsa (TLS1.3) tls TLS_AES_256_GCM_SHA384 (Exim 4.99.5) (envelope-from ) id 1xIY0v-0000000Doky-2uO5; Sun, 18 Oct 2026 21:01:53 +0000 Message-ID: Subject: Re: [RFC PATCH v3 8/8] mm/gup: batch contiguous same-folio PTEs into one refcount grab From: Rik van Riel To: Yuan-Hao Hsu 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 Date: Sun, 18 Oct 2026 17:01:53 -0400 In-Reply-To: <20261018182652.691-1-aa9736195201@gmail.com> References: <20260811025157.1632867-1-riel@surriel.com> <20260811025157.1632867-9-riel@surriel.com> <20261018182652.691-1-aa9736195201@gmail.com> Autocrypt: addr=riel@surriel.com; prefer-encrypt=mutual; keydata=mQENBFIt3aUBCADCK0LicyCYyMa0E1lodCDUBf6G+6C5UXKG1jEYwQu49cc/gUBTTk33A eo2hjn4JinVaPF3zfZprnKMEGGv4dHvEOCPWiNhlz5RtqH3SKJllq2dpeMS9RqbMvDA36rlJIIo47 Z/nl6IA8MDhSqyqdnTY8z7LnQHqq16jAqwo7Ll9qALXz4yG1ZdSCmo80VPetBZZPw7WMjo+1hByv/ lvdFnLfiQ52tayuuC1r9x2qZ/SYWd2M4p/f5CLmvG9UcnkbYFsKWz8bwOBWKg1PQcaYHLx06sHGdY dIDaeVvkIfMFwAprSo5EFU+aes2VB2ZjugOTbkkW2aPSWTRsBhPHhV6dABEBAAG0HlJpayB2YW4gU mllbCA8cmllbEByZWRoYXQuY29tPokBHwQwAQIACQUCW5LcVgIdIAAKCRDOed6ShMTeg05SB/986o gEgdq4byrtaBQKFg5LWfd8e+h+QzLOg/T8mSS3dJzFXe5JBOfvYg7Bj47xXi9I5sM+I9Lu9+1XVb/ r2rGJrU1DwA09TnmyFtK76bgMF0sBEh1ECILYNQTEIemzNFwOWLZZlEhZFRJsZyX+mtEp/WQIygHV WjwuP69VJw+fPQvLOGn4j8W9QXuvhha7u1QJ7mYx4dLGHrZlHdwDsqpvWsW+3rsIqs1BBe5/Itz9o 6y9gLNtQzwmSDioV8KhF85VmYInslhv5tUtMEppfdTLyX4SUKh8ftNIVmH9mXyRCZclSoa6IMd635 Jq1Pj2/Lp64tOzSvN5Y9zaiCc5FucXtB9SaWsgdmFuIFJpZWwgPHJpZWxAc3VycmllbC5jb20+iQE +BBMBAgAoBQJSLd2lAhsjBQkSzAMABgsJCAcDAgYVCAIJCgsEFgIDAQIeAQIXgAAKCRDOed6ShMTe g4PpB/0ZivKYFt0LaB22ssWUrBoeNWCP1NY/lkq2QbPhR3agLB7ZXI97PF2z/5QD9Fuy/FD/jddPx KRTvFCtHcEzTOcFjBmf52uqgt3U40H9GM++0IM0yHusd9EzlaWsbp09vsAV2DwdqS69x9RPbvE/Ne fO5subhocH76okcF/aQiQ+oj2j6LJZGBJBVigOHg+4zyzdDgKM+jp0bvDI51KQ4XfxV593OhvkS3z 3FPx0CE7l62WhWrieHyBblqvkTYgJ6dq4bsYpqxxGJOkQ47WpEUx6onH+rImWmPJbSYGhwBzTo0Mm G1Nb1qGPG+mTrSmJjDRxrwf1zjmYqQreWVSFEt26tBpSaWsgdmFuIFJpZWwgPHJpZWxAZmIuY29tP okBPgQTAQIAKAUCW5LbiAIbIwUJEswDAAYLCQgHAwIGFQgCCQoLBBYCAwECHgECF4AACgkQznneko TE3oOUEQgAsrGxjTC1bGtZyuvyQPcXclap11Ogib6rQywGYu6/Mnkbd6hbyY3wpdyQii/cas2S44N cQj8HkGv91JLVE24/Wt0gITPCH3rLVJJDGQxprHTVDs1t1RAbsbp0XTksZPCNWDGYIBo2aHDwErhI omYQ0Xluo1WBtH/UmHgirHvclsou1Ks9jyTxiPyUKRfae7GNOFiX99+ZlB27P3t8CjtSO831Ij0Ip QrfooZ21YVlUKw0Wy6Ll8EyefyrEYSh8KTm8dQj4O7xxvdg865TLeLpho5PwDRF+/mR3qi8CdGbkE c4pYZQO8UDXUN4S+pe0aTeTqlYw8rRHWF9TnvtpcNzZw== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.2 (3.60.2-1.fc44) MIME-Version: 1.0 X-Rspamd-Queue-Id: A066340005 X-Stat-Signature: w65f3awywzyh73jj9w8juo6kszqru6kb X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1792357346-630445 X-HE-Meta: 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 JcdaWKib GeAjwItNE3d7cSMfaUuKDZyu0fNS8QkfR/F+o6DJQedolaDuYfcoaVrBtIhaiPuNNUcV2d18n3jYBMtAhQYRtS9hcAzSWvGK+e3GngPkpEs39cAyGu35CuoV8gKhTcaO9MLWS/cZbawvovpttg0ujB3cRo3jQxiSMChM1OqsK3VbZq/u43Ws3wd4pjd1EVawlxD4sfHkdv+JyzNsKtfftzW/z3N2SSaxCzG0VRQJ0kdBPP2WKy2QxQvgPiUuAZcFNZ+x7yh6Kw6TbemlrExEzdxh19A== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 2026-10-19 at 02:26 +0800, Yuan-Hao Hsu wrote: > 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. >=20 > 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. >=20 > 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): >=20 > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 before=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 after > =C2=A0 folio_mark_accessed=C2=A0 512 per call=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0 32 per call > =C2=A0 after 1st call=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 32 folios activ= e=C2=A0 32 referenced, 0 active > =C2=A0 after 2nd call=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 32 active=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 32 active >=20 > 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.=C2=A0 It is still a visible change in > aging for anything that reaches these folios through get_user_pages() > rather than the fast path. >=20 Nice catch. You are right that this should be in the changelog! I'll get that in for v4. --=20 All Rights Reversed.