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h=From:To:Cc:Subject:Date:From; b=gT8rV42Mxd4wvgf5OaeZErHCRVkQ1VYUGuARq+ONMgYtfMHQ1IiZdToGo+9gexoLI Fi3Ewq0j5MAodsRqKhN4Xd68ynhMfMZKfmRjmvURCvjjE1/KFGtViKArO9PZA9W3NJ RnRAhNrtDGa9jGjWHDu5s3xQnVEi/V9YBQ8Q2OFE= From: Dev Jain To: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, hughd@google.com, chrisl@kernel.org, kasong@tencent.com Cc: Dev Jain , riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, qi.zheng@linux.dev, shakeel.butt@linux.dev, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, rppt@kernel.org, surenb@google.com, mhocko@suse.com, baolin.wang@linux.alibaba.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, youngjun.park@lge.com, pfalcato@suse.de, ryan.roberts@arm.com, anshuman.khandual@arm.com Subject: [PATCH v3 0/9] Optimize anonymous large folio unmapping Date: Wed, 6 May 2026 15:14:55 +0530 Message-Id: <20260506094504.2588857-1-dev.jain@arm.com> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: E036214000F X-Rspam-User: X-Stat-Signature: 9feah71ph5499eibnfnnm9borhw7kaic X-HE-Tag: 1778060720-213059 X-HE-Meta: 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 1fNRH3CV fPULhEehfZC5fRCgYEF0Bu3ssTBFyBCDPTw0pCZu20Th+67GmBHheXZZhVs6lzYs55YkEgcbBhxUNuFdCHLkZvAONrhaIKNG1e+An57PT5fyeVpVTTh5sBQxJ4HG1Gdte5UubwZeF3WFoaOEE7tzTtiBPFTz179J/e3q/wR1AEVz/vgi+HfgBVX2X3A== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Speed up unmapping of anonymous large folios by clearing the ptes, and setting swap ptes, in one go. The following benchmark (stolen from Barry at [1]) is used to measure the time taken to swapout 256M worth of memory backed by 64K large folios: #define _GNU_SOURCE #include #include #include #include #include #include #include #define SIZE_MB 256 #define SIZE_BYTES (SIZE_MB * 1024 * 1024) int main() { void *addr = mmap(NULL, SIZE_BYTES, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if (addr == MAP_FAILED) { perror("mmap failed"); return 1; } memset(addr, 0, SIZE_BYTES); struct timespec start, end; clock_gettime(CLOCK_MONOTONIC, &start); if (madvise(addr, SIZE_BYTES, MADV_PAGEOUT) != 0) { perror("madvise(MADV_PAGEOUT) failed"); munmap(addr, SIZE_BYTES); return 1; } clock_gettime(CLOCK_MONOTONIC, &end); long duration_ns = (end.tv_sec - start.tv_sec) * 1e9 + (end.tv_nsec - start.tv_nsec); printf("madvise(MADV_PAGEOUT) took %ld ns (%.3f ms)\n", duration_ns, duration_ns / 1e6); munmap(addr, SIZE_BYTES); return 0; } Performance as measured on a Linux VM on Apple M3 (arm64): Vanilla - Mean: 37401913 ns, std dev: 12% Patched - Mean: 17420282 ns, std dev: 11% No regression observed on 4K folios. Performance as measured on bare metal x86: Vanilla - mean: 54986286 ns, std dev: 1.5% Patched - mean: 51930795 ns, std dev: 3% Interestingly, no obvious improvement is observed on x86, hinting that the benefit lies mainly in the reduction of ptep_get() calls and the reduction of TLB flushes during contpte-unfolding, on arm64. No regression is observed on 4K folios on x86 too. --- Applies on mm-unstable (2d565cbaafd4). v2->v3: Mostly a resend after merge window. Some minor changes: - Match kerneldoc parameter with function parameter (pte -> ptep) - Mention change BUG->WARN in patch description - Rename walk_done -> exit_walk in patch 2 - v1->v2: - Keep nr_pages as unsigned long - Add patch 2 - Rename some functions, make return type bool for functions returning 0/1 - Drop page_vma_mapped_walk_jump - this is implicitly handled - Drop likely() - Add folio_dup/put_swap_pages, do subpage -> page - Shorten the kerneldoc to remove unnecessary information - keep it aligned with analogous functions - Put clear_pages_anon_exclusive to mm.h - Some more refactoring in last patch with finish_folio_unmap Dev Jain (9): mm/rmap: initialize nr_pages to 1 at loop start in try_to_unmap_one mm/rmap: refactor hugetlb pte clearing in try_to_unmap_one mm/rmap: refactor some code around lazyfree folio unmapping mm/memory: Batch set uffd-wp markers during zapping mm/rmap: batch unmap folios belonging to uffd-wp VMAs mm/swapfile: Add batched version of folio_dup_swap mm/swapfile: Add batched version of folio_put_swap mm/rmap: Add batched version of folio_try_share_anon_rmap_pte mm/rmap: enable batch unmapping of anonymous folios include/linux/mm.h | 11 ++ include/linux/mm_inline.h | 34 ++-- include/linux/rmap.h | 27 ++- mm/internal.h | 26 +++ mm/memory.c | 26 +-- mm/mprotect.c | 17 -- mm/rmap.c | 405 ++++++++++++++++++++++++-------------- mm/shmem.c | 8 +- mm/swap.h | 23 ++- mm/swapfile.c | 42 ++-- 10 files changed, 383 insertions(+), 236 deletions(-) -- 2.34.1