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t=1790255516; bh=omnc/jiGce2ioWghxdLYMfvILVqD+Qx1+Ygyy+n/n2I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Cqw+z1JRNnoGVg2M6BZ0XIIofy3CKrxfcxsiHv5K+w04E+MA396UFlL/9MTxcEloj ud6CPr2NiTciVXHDU2JreHt0oDkzaKPTyWyHjt7MGCOjQR57BRSR//s31IDbO3h2TW 1507rdZMwHyYs34HsTPCcSn5rAfhP9nMsXTEXPHw= From: Dev Jain To: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, hughd@google.com, chrisl@kernel.org, kasong@tencent.com, davem@davemloft.net, andreas@gaisler.com Cc: Dev Jain , riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, lance.yang@linux.dev, baolin.wang@linux.alibaba.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, baoquan.he@linux.dev, baohua@kernel.org, youngjun.park@lge.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, pfalcato@suse.de, jgg@ziepe.ca, thuth@redhat.com, sparclinux@vger.kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com Subject: [PATCH v3 4/9] mm/rmap: Add batched version of folio_try_share_anon_rmap_pte Date: Thu, 24 Sep 2026 13:09:32 +0000 Message-ID: <20260924131106.1730494-5-dev.jain@arm.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260924131106.1730494-1-dev.jain@arm.com> References: <20260924131106.1730494-1-dev.jain@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 25B24140008 X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: tiunk3jeq8euywndffsehxhyb8dicwoo X-HE-Tag: 1790255516-823922 X-HE-Meta: U2FsdGVkX18EZF6MNjJgEiH+u7AQSsWfX93L4L1h6nbu90KNCTPXkSa41iKxdJCx6/5JZ/Nlle5VZc7i/m7D+tFgbFhGSZBmOGWdb7zSCq2gGqA+IUuu8CXjPIe6hR5z4yDw6IrMp4bFu4rLYZwheRZkIDvtmf2yVx9XO6dUtxDMU/5Vxrp+aheseMHKViL1e3TlTbw3kJvf961fQrFYaDD40hz277udozv1831KLCCER9gB5iVFqUiWlkDFfquykbaPYg9ECGGn5S/+4+lfROv8oGIgEy1hSiN2s0S3N4exxuCA2ncORdsRnFKuz4jyqHSHJB4iaX5ZdZEI2tTtSAwXK4wONCpxog9AwT7fB9X6Ikf+5ONAO9r9FwIP728hvfjtzjD9WtZH73VN+k7dpMfqniGv6p6ftQs40DOihCqXwcTlWFfA+uOr3+MYCEeWoJPR2u2f0BSBHJG4NiclEg97pz5ENgMeTxJTlJax3rfv4/GlZ5SRpc6VpM0Lh7I9N0WpLC0tWsD2IMpRvCwO3cd0aNYNjMbRPReHrcevRVZ5yHLktv7ksYNHKAYM1BaA3aeobGIUNUq33STXovCLf7BFTskp04ZbOx3iPEnTP6VH4HfrquiqRhji+LQN0U97pDJp2z59bi/C60nkz1o8bxXPHAhtoJ4T/DKcatlvUmS5x4QcWpb/RIUEf9vDHJ4Qrv+BEl7WUAvLE98kPGPcxgJQABAF1w5VrZIzYP4fOXF+9MOG1NSoPQvRHcmvdHZExYAio0Gs4K2D9yLcwPWFbzPnlUeKJd0BVQaRqJ4jmhDn0ZZYNic77FyH86tozXgcmXo96zIpAmdE4i9yfwyPAY6e5q3lAxM+H9K+WON800+U6inuhcKGxA3DgbXrHShPHh8ptGDJZBQGn8zqi7eN4SMtLBZY6Ab9hX1oe4wDqrbc4ofzlxBjCuFxeJXLJW4S9gtlGmRuDag04UHdSmQ 31sDs8fn 6bS6ux9Ce4Pd9Io0Mp2o7bgCWK8ySW05SCcRVp+mYYW4H5RmqolMj44uiq0jSZsS9dN/INfIVeQ0FFTqNqCmlQCkVLp6UMEuDdeBbY4/c9hqneFQCB36XollGcCEyY0we93ckfrTmslmQ1s7vT5mvdWSanYXcu9ikoezBEXuL2+jDSmK2PlQVzHa1B3LpP85Z/0y7ZJG/h1sH93Vws6Wv97VCTtESyZzv8b7KKldhYYCFBBjodSWfRmKAxnjjAsQtQLRKXjz9rcZMaTBoyTIte/JzPQItQA/5ChcVs5tORPaozjM= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: To enable batched unmapping of anonymous folios, we need to handle the sharing of exclusive pages. Hence, a batched version of folio_try_share_anon_rmap_pte is required. Currently, the sole purpose of nr_pages in __folio_try_share_anon_rmap is to do some rmap sanity checks. Now, clear the PageAnonExclusive bit on a batch of nr_pages. Refactor the function such that the clearing of the bit can be done at one place without duplication. Note that __folio_try_share_anon_rmap can receive nr_pages == HPAGE_PMD_NR from the PMD path, but currently we only clear the bit on the head page. Retain this behaviour by setting nr_pages = 1 in case the caller is folio_try_share_anon_rmap_pmd. While at it, convert nr_pages to unsigned long to future-proof from overflow in case P4D-huge mappings etc get supported down the road. I haven't made such a change in each function receiving nr_pages in try_to_unmap_one - perhaps this can be done incrementally. Add two WARN's: check that the batch is entirely exclusive (for PMD callers, need to check only head page), and that there are only PTE/PMD paths converging into __folio_try_share_anon_rmap. Signed-off-by: Dev Jain --- include/linux/rmap.h | 56 ++++++++++++++++++++++++++++++-------------- 1 file changed, 39 insertions(+), 17 deletions(-) diff --git a/include/linux/rmap.h b/include/linux/rmap.h index 62ef511a6175a..91b5763ef466f 100644 --- a/include/linux/rmap.h +++ b/include/linux/rmap.h @@ -723,17 +723,23 @@ static inline int folio_try_dup_anon_rmap_pmd(struct folio *folio, } static __always_inline int __folio_try_share_anon_rmap(struct folio *folio, - struct page *page, int nr_pages, enum pgtable_level level) + struct page *page, unsigned long nr_pages, enum pgtable_level level) { + /* device private folios cannot get pinned via GUP. */ + const bool pinnable = !folio_is_device_private(folio); + VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio); VM_WARN_ON_FOLIO(!PageAnonExclusive(page), folio); + __folio_rmap_sanity_checks(folio, page, nr_pages, level); - /* device private folios cannot get pinned via GUP. */ - if (unlikely(folio_is_device_private(folio))) { - ClearPageAnonExclusive(page); - return 0; - } + VM_WARN_ON_ONCE(level != PGTABLE_LEVEL_PTE && level != PGTABLE_LEVEL_PMD); + + /* We only clear anon-exclusive from head page of PMD folio. */ + if (level == PGTABLE_LEVEL_PMD) + nr_pages = 1; + + VM_WARN_ON_FOLIO(page_anon_exclusive_batch(0, nr_pages, page, true) != nr_pages, folio); /* * We have to make sure that when we clear PageAnonExclusive, that @@ -777,29 +783,38 @@ static __always_inline int __folio_try_share_anon_rmap(struct folio *folio, * so we use explicit ones here. */ - /* Paired with the memory barrier in try_grab_folio(). */ - if (IS_ENABLED(CONFIG_HAVE_GUP_FAST)) - smp_mb(); + if (likely(pinnable)) { + /* Paired with the memory barrier in try_grab_folio(). */ + if (IS_ENABLED(CONFIG_HAVE_GUP_FAST)) + smp_mb(); - if (unlikely(folio_maybe_dma_pinned(folio))) - return -EBUSY; - ClearPageAnonExclusive(page); + if (unlikely(folio_maybe_dma_pinned(folio))) + return -EBUSY; + } + + for (;;) { + ClearPageAnonExclusive(page); + if (--nr_pages == 0) + break; + page++; + } /* * This is conceptually a smp_wmb() paired with the smp_rmb() in * gup_must_unshare(). */ - if (IS_ENABLED(CONFIG_HAVE_GUP_FAST)) + if (likely(pinnable) && IS_ENABLED(CONFIG_HAVE_GUP_FAST)) smp_mb__after_atomic(); return 0; } /** - * folio_try_share_anon_rmap_pte - try marking an exclusive anonymous page - * mapped by a PTE possibly shared to prepare + * folio_try_share_anon_rmap_ptes - try marking exclusive anonymous pages + * mapped by PTEs possibly shared to prepare * for KSM or temporary unmapping * @folio: The folio to share a mapping of - * @page: The mapped exclusive page + * @page: The first mapped exclusive page of the batch in the folio + * @nr_pages: The number of pages to share in the folio (batch size) * * The caller needs to hold the page table lock and has to have the page table * entries cleared/invalidated. @@ -815,10 +830,17 @@ static __always_inline int __folio_try_share_anon_rmap(struct folio *folio, * Returns 0 if marking the mapped page possibly shared succeeded. Returns * -EBUSY otherwise. */ +static inline int folio_try_share_anon_rmap_ptes(struct folio *folio, + struct page *page, unsigned long nr_pages) +{ + return __folio_try_share_anon_rmap(folio, page, nr_pages, + PGTABLE_LEVEL_PTE); +} + static inline int folio_try_share_anon_rmap_pte(struct folio *folio, struct page *page) { - return __folio_try_share_anon_rmap(folio, page, 1, PGTABLE_LEVEL_PTE); + return folio_try_share_anon_rmap_ptes(folio, page, 1); } /** -- 2.43.0