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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4535e97ac4asm173506505e9.3.2025.06.24.05.55.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 24 Jun 2025 05:55:19 -0700 (PDT) Message-ID: Date: Tue, 24 Jun 2025 14:55:18 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 3/4] mm: Support batched unmap for lazyfree large folios during reclamation To: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org Cc: baolin.wang@linux.alibaba.com, chrisl@kernel.org, ioworker0@gmail.com, kasong@tencent.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, lorenzo.stoakes@oracle.com, ryan.roberts@arm.com, v-songbaohua@oppo.com, x86@kernel.org, ying.huang@intel.com, zhengtangquan@oppo.com References: <20250214093015.51024-1-21cnbao@gmail.com> <20250214093015.51024-4-21cnbao@gmail.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250624_055524_240072_8CAC9CEA X-CRM114-Status: GOOD ( 18.73 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 14.02.25 10:30, Barry Song wrote: > From: Barry Song > > Currently, the PTEs and rmap of a large folio are removed one at a time. > This is not only slow but also causes the large folio to be unnecessarily > added to deferred_split, which can lead to races between the > deferred_split shrinker callback and memory reclamation. This patch > releases all PTEs and rmap entries in a batch. > Currently, it only handles lazyfree large folios. > > The below microbench tries to reclaim 128MB lazyfree large folios > whose sizes are 64KiB: > > #include > #include > #include > #include > > #define SIZE 128*1024*1024 // 128 MB > > unsigned long read_split_deferred() > { > FILE *file = fopen("/sys/kernel/mm/transparent_hugepage" > "/hugepages-64kB/stats/split_deferred", "r"); > if (!file) { > perror("Error opening file"); > return 0; > } > > unsigned long value; > if (fscanf(file, "%lu", &value) != 1) { > perror("Error reading value"); > fclose(file); > return 0; > } > > fclose(file); > return value; > } > > int main(int argc, char *argv[]) > { > while(1) { > volatile int *p = mmap(0, SIZE, PROT_READ | PROT_WRITE, > MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); > > memset((void *)p, 1, SIZE); > > madvise((void *)p, SIZE, MADV_FREE); > > clock_t start_time = clock(); > unsigned long start_split = read_split_deferred(); > madvise((void *)p, SIZE, MADV_PAGEOUT); > clock_t end_time = clock(); > unsigned long end_split = read_split_deferred(); > > double elapsed_time = (double)(end_time - start_time) / CLOCKS_PER_SEC; > printf("Time taken by reclamation: %f seconds, split_deferred: %ld\n", > elapsed_time, end_split - start_split); > > munmap((void *)p, SIZE); > } > return 0; > } > > w/o patch: > ~ # ./a.out > Time taken by reclamation: 0.177418 seconds, split_deferred: 2048 > Time taken by reclamation: 0.178348 seconds, split_deferred: 2048 > Time taken by reclamation: 0.174525 seconds, split_deferred: 2048 > Time taken by reclamation: 0.171620 seconds, split_deferred: 2048 > Time taken by reclamation: 0.172241 seconds, split_deferred: 2048 > Time taken by reclamation: 0.174003 seconds, split_deferred: 2048 > Time taken by reclamation: 0.171058 seconds, split_deferred: 2048 > Time taken by reclamation: 0.171993 seconds, split_deferred: 2048 > Time taken by reclamation: 0.169829 seconds, split_deferred: 2048 > Time taken by reclamation: 0.172895 seconds, split_deferred: 2048 > Time taken by reclamation: 0.176063 seconds, split_deferred: 2048 > Time taken by reclamation: 0.172568 seconds, split_deferred: 2048 > Time taken by reclamation: 0.171185 seconds, split_deferred: 2048 > Time taken by reclamation: 0.170632 seconds, split_deferred: 2048 > Time taken by reclamation: 0.170208 seconds, split_deferred: 2048 > Time taken by reclamation: 0.174192 seconds, split_deferred: 2048 > ... > > w/ patch: > ~ # ./a.out > Time taken by reclamation: 0.074231 seconds, split_deferred: 0 > Time taken by reclamation: 0.071026 seconds, split_deferred: 0 > Time taken by reclamation: 0.072029 seconds, split_deferred: 0 > Time taken by reclamation: 0.071873 seconds, split_deferred: 0 > Time taken by reclamation: 0.073573 seconds, split_deferred: 0 > Time taken by reclamation: 0.071906 seconds, split_deferred: 0 > Time taken by reclamation: 0.073604 seconds, split_deferred: 0 > Time taken by reclamation: 0.075903 seconds, split_deferred: 0 > Time taken by reclamation: 0.073191 seconds, split_deferred: 0 > Time taken by reclamation: 0.071228 seconds, split_deferred: 0 > Time taken by reclamation: 0.071391 seconds, split_deferred: 0 > Time taken by reclamation: 0.071468 seconds, split_deferred: 0 > Time taken by reclamation: 0.071896 seconds, split_deferred: 0 > Time taken by reclamation: 0.072508 seconds, split_deferred: 0 > Time taken by reclamation: 0.071884 seconds, split_deferred: 0 > Time taken by reclamation: 0.072433 seconds, split_deferred: 0 > Time taken by reclamation: 0.071939 seconds, split_deferred: 0 > ... > > Signed-off-by: Barry Song > --- > mm/rmap.c | 72 ++++++++++++++++++++++++++++++++++++++----------------- > 1 file changed, 50 insertions(+), 22 deletions(-) > > diff --git a/mm/rmap.c b/mm/rmap.c > index 89e51a7a9509..8786704bd466 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1781,6 +1781,25 @@ void folio_remove_rmap_pud(struct folio *folio, struct page *page, > #endif > } > > +/* We support batch unmapping of PTEs for lazyfree large folios */ > +static inline bool can_batch_unmap_folio_ptes(unsigned long addr, > + struct folio *folio, pte_t *ptep) > +{ > + const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY; > + int max_nr = folio_nr_pages(folio); Let's assume we have the first page of a folio mapped at the last page table entry in our page table. What prevents folio_pte_batch() from reading outside the page table? -- Cheers, David / dhildenb