From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=217.140.110.172 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794227556; b=le/yghcwuX6zc9SPjNUJDgFimmyXX9qdAEeyp2jAlRbFgpW+62ggeIv/MyFJ7qUPN1RS xOOFxRuYyyqrMKxkDUeSMF2EUaQmJWGnHnJH8mXQDHmoOMMulmCqEOcc+OBkh1R2ZNPLe UPljNoDkPxO6W2F9tzwYVAEo1wEseHATIbeAxvejPk4uoRHrvtMHTHUwQ9IXsgbTcQxm9 pjVgS4cyVPJFtI2V9s96zLLJWkO7wfLxIgemQUL+jCeqWzeRLFEGh9A7v3ZIarsKdYklV S1eqMz1ocxIYEuWUzV0odqjkZYsCq1ht9MJmBI6jXmVbg4yW52r5snMb0Z+kOtBg3Dg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794227556; h=DMARC-Filter:Received:Received:DKIM-Signature:From:Subject:Date: Message-Id:MIME-Version:Content-Type:Content-Transfer-Encoding: X-B4-Tracking:To:Cc:X-Mailer:X-Developer-Signature:X-Developer-Key; bh=udxm0MTbbrdZXwgUGf8nDE4esUDzC+N90hU7KZ64eOw=; b=NHMmtrMroeBgtZQJeqXFfRXXaZtKeV/OgIc2Oc9m/d+p3D3P3pbGQL1XHQ5wnCmxH4cT XyV+aL9lK5ON/9mv6dku71MlTk7GqYwU5m/my4vaF9Jy8kG/NDDNXEvTPmakEPgXc3w/1 NQqMMtWOw0GVmJuvXo4p2qYPTIhP/x0SsDGV9eWNX4l2wnPP6d4XTwW15lmWULmL79pIH WRvdVSfjR5IjZygxuWr7h9F0oEbvd8lMl4BAbig3AB68v90I5+sDuF7COgnl/ieGRCTNT s4s/T314Im7a4IhrlN5LjGsjEA4VEq+il3DOgYgbSFGBbWeKRsR/3Km5ZITU1WwfrDA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass header.d=arm.com header.i=@arm.com header.a=rsa-sha256 header.s=foss header.b=jVUw9NIZ; arc=none smtp.remote-ip=217.140.110.172 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id D45726083607; Mon, 9 Nov 2026 12:32:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org D45726083607 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=arm.com header.i=@arm.com header.a=rsa-sha256 header.s=foss header.b=jVUw9NIZ Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D6E7F1516; Mon, 9 Nov 2026 04:32:30 -0800 (PST) Received: from e129823.arm.com (e129823.arm.com [10.2.213.3]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D685A3F632; Mon, 9 Nov 2026 04:32:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1794227553; bh=QEIH/LF9UuKjHrGluytD0ntXd7KX++xnyDqOTz3eQxg=; h=From:Subject:Date:To:Cc:From; b=jVUw9NIZJQgWxyUNHKdc5Exo6aZc4V67EokCep5T4IuCtIkIYUkyvE6/dwyws9SRF F4Q+MlU9oCT1yg6ZcQGut0uAj7EhqwWgdpFhM6VtJlZ3BIij13jiAL63Wbv4OXw2rw BPaAPIpdz+wt4M2bhue6a4U2/Fwh4lMLlKexi9OQ= From: Yeoreum Yun Subject: [PATCH v3 0/6] mm: gup: batch PTE-mapped large folios in gup_fast_pte_range() Date: Mon, 09 Nov 2026 12:32:24 +0000 Message-Id: <20261109-refactor_gup_fast-v3-0-2aaef02df0e1@arm.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-B4-Tracking: v=1; b=H4sIAFi98WoC/33PwU7DMAwG4FeZcibIjnHa7sR7IDSlbrLlsHVKR gWa+u64Q2IHVo5O/P3WfzU1lhyr2W6upsQp1zyedKCnjZFDOO2jzYPOxoHzCMi2xBTkMpbd/uO 8S6FebM8cKXFHgzij7qwr+fOW+fau8yFX3f+6nZhwef0vbUILliLGxNz41qfXUI7PMh6X6B/nY M1J6hqHXRg8yQOHaw6AQyCtwch/Ha3e89D0DRC3Gv7rls6Tu/fUv0feqe8FgwC20tLL3c/z/A3 MG92wmAEAAA== To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Jason Gunthorpe , John Hubbard , Peter Xu , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Andrew Morton , David Hildenbrand , Rik van Riel , Yuan-Hao Hsu , Yeoreum Yun , stable@vger.kernel.org X-Mailer: b4 0.13.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=4382; i=yeoreum.yun@arm.com; h=from:subject:message-id; bh=QEIH/LF9UuKjHrGluytD0ntXd7KX++xnyDqOTz3eQxg=; b=owEB7QES/pANAwAKAW3Vw9FaxTEzAcsmYgBq8b1cwMlPTqUm+x5Hxjglzdl5JcKEFbgfCrTWS TJh461BZ/GJAbMEAAEKAB0WIQQtg+CS3QUzuFh1pJ1t1cPRWsUxMwUCavG9XAAKCRBt1cPRWsUx M9Y3C/4/1RLK0kmQkgFGc/uX6lWK1ZEh6vA4r9A2qySbAcekJskXN3a0cqbYnYyZK6R/OWWD6uu 56YEDOfgDN0kDoeNB2wrJjqUTis7CG1JdPT7Ab1Eeen4/M0XDlTHB8hmume5z+p/NWKWFEoCBMp 0BaN0G45miLkLN58dHZk8xzeye/VLwmm7+KAkLfx3HvNDk/kQqoYrkSugMwQdvT0sFLf0mh5yFQ 66Z5j5c5gZKnE3vSawjpSWJtkmsofclWDmfCn2gg7y0FnJLMMX8pESvnjpCJv9ZxevUVQVaUD+6 uH6OoVZbyhZK7sHzA4HY8iM4iAnCttvb07jLW/XTlXIrz2OmemCuCkXOJlgspqrq7DPBgHGf9xd g3GAu5p0EAJjOU/LF19RLBIg5c+QlVNtky0OM8AKx7H9x7BCHb8Ppe5l5hViDX5UAxvc7dl0ybB yiF/kQbTOqnqo6gZ6zfwEwjdRteIBD1o71IFlwpedaWPrhU4S97zCqrxO/VI916q5CgCQ= X-Developer-Key: i=yeoreum.yun@arm.com; a=openpgp; fpr=2D83E092DD0533B85875A49D6DD5C3D15AC53133 GUP-fast grabs a PTE-mapped large folio one page at a time. Every PTE costs a try_grab_folio_fast() (a refcount cmpxchg, plus the pincount atomic, a full barrier and a node stat update for FOLL_PIN), a gup_fast_folio_allowed() and a folio_set_referenced(), so a 64 kB mTHP pays sixteen of each and a PTE-mapped 2 MB THP pays 512. The users are the hot ones: iov_iter_extract_user_pages() pins every O_DIRECT buffer through pin_user_pages_fast(), io_uring registers its buffers through it, and so does RDMA memory registration. With mTHP those buffers are PTE-mapped large folios. After the head page has been grabbed and verified, extend the run to the following PTEs that map the next pages of the same folio with the same protection bits, take the remaining references for the run with try_grab_folio(), and fill pages[] from the run. The PTEs of the run are read while the reference on the folio is held, so the folio can neither be collapsed, freed nor split underneath the scan. A read-only run of an anonymous folio stops at the first page that gup_must_unshare() rejects, so the per-page exclusivity guarantee for FOLL_PIN is kept. folio_pte_batch_flags() does the scan. It reads the entries with ptep_get(), which is not safe without the page table lock on CONFIG_GUP_GET_PXX_LOW_HIGH (x86 PAE, mips32, sh) or with arm64 contpte, and GUP-fast reads every PTE with ptep_get_lockless() for that reason. Add FPB_LOCKLESS to make the helper do the same; it is inlined per call site, so the other callers do not change. The order-0 path keeps its instruction sequence. The folio flags are tested before folio_set_referenced() on purpose: a load of the flags right after that locked instruction cost about 25% on order-0 pages in the gup_test benchmark below, and reading them first brings that path back to the baseline. gup_test ioctl over a 256 MB anonymous region, FOLL_WRITE, 65536 pages per call, median of 15 runs, two baseline boots / one patched boot, on an x86-64 VM: get_user_pages_fast() pin_user_pages_fast() before after before after 4 kB pages 849/789 us 783 us 1174/1138 us 1094 us 64 kB mTHP 812/811 us 126 us 1215/1113 us 188 us 1 MB mTHP 799/774 us 59 us 1185/1077 us 64 us 2 MB THP, PTE-mapped 803/786 us 57 us 1159/1120 us 58 us 2 MB THP, PMD-mapped 42/40 us 40 us 46/41 us 42 us fio O_DIRECT randread of a null_blk device (CPU bound) with the I/O buffer in 64 kB mTHP, median of 15 five-second runs: bs=1M psync 126.2/125.6 GB/s -> 220.6 GB/s bs=1M io_uring, iodepth 16 71.2/71.6 GB/s -> 112.1 GB/s bs=64k io_uring, iodepth 16 50.2/50.7 GB/s -> 60.1 GB/s IORING_REGISTER_BUFFERS of 1 GB, median of 15: 64 kB mTHP 6179/5998 us -> 1599 us 1 MB mTHP 5790/5801 us -> 893 us 4 kB pages 7173/6741 us -> 6763 us --- Changes in v3: - move gup_must_unshare() and INTERNAL_GUP_FLAGS from internal.h to gup.c - drop the folio_pte_batch_flags() patch for shadow-stack. - ignore VM_HUGEPAGE for shadow-stack via madvise(). - add r-b / a-b tags. - Link to v2: https://lore.kernel.org/r/20261102-refactor_gup_fast-v2-0-bc1ac018c834@arm.com Changes in v2: - fix exceptional case for shstk on x86. - remove redendant check for pmd change in each pte barch. - Link to v1: https://lore.kernel.org/all/20260917083747.786-1-aa9736195201@gmail.com/ --- Yeoreum Yun (5): mm: khugepaged: ignore MADV_HUGEPAGE for shadow stacks mm: gup: clarify a reason to check pte/pmd in gup_fast_pte_range() mm: gup: move gup_must_unshare() and INTERNAL_GUP_FLAGS to gup.c mm: gup: introduce gup_unshared_pages() mm: gup: batch PTE-mapped large folios in gup_fast_pte_range() Yuan-Hao Hsu (1): mm: internal: introduce FPB_LOCKLESS for folio_pte_batch_flags() mm/gup.c | 185 +++++++++++++++++++++++++++++++++++++++++++++----------- mm/internal.h | 78 +++--------------------- mm/khugepaged.c | 3 + 3 files changed, 159 insertions(+), 107 deletions(-) --- base-commit: b3710a1d0f145a4f6f1d44fdaff56a6af8cffe89 change-id: 20261015-refactor_gup_fast-b55e3f593dc2 Best regards, -- Sincerely, Yeoreum Yun