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Fri, 17 Jan 2025 09:30:36 +0800 Message-ID: Date: Fri, 17 Jan 2025 09:30:33 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 4/4] mm: Avoid splitting pmd for lazyfree pmd-mapped THP in try_to_unmap To: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org Cc: chrisl@kernel.org, david@redhat.com, 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: <20250115033808.40641-1-21cnbao@gmail.com> <20250115033808.40641-5-21cnbao@gmail.com> From: Baolin Wang In-Reply-To: <20250115033808.40641-5-21cnbao@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 1DD9A1C000C X-Stat-Signature: 4646di4i9wtgzuotdbjjpn6oq3y8dxw9 X-Rspamd-Server: rspam08 X-Rspam-User: X-HE-Tag: 1737077440-157219 X-HE-Meta: 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 2xDJzJFL T8nR5qCEiy/g1FAoYneOfq7QPN3COa+09zSSEGtwQPYjENtdO/h7Zdc6woADFooqDiZAIXxiUtAM2nwmFzBkyuXkkRSi5REiZzFOedph+EIeCJZODgs5SPLK4zzlwNewQ8rmZ3SS7cKHXP6gkHxGudgfOt5qMysviBPVTjAYWM0Yci5D1FgphYgPp/26VZk8et7Tt0VWOzMzVGMWw+Yj23m8WP7pKzZGNC+2adlDildSqLkigkkrMOaKNxENZP6Pg0LcXscn3UvxUHl73XoEKsfH9cxjFR6Ot6V4pasGczwbjKpC9WbHHOOe0w+6Khv3kOI90DamPxX8iJdBwMY+4hnQshfs39EKaX7TfmMEhSVQYFohrcL3dnXRPIirvefPqXx2ATH5PYAUdL4U= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000398, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2025/1/15 11:38, Barry Song wrote: > From: Barry Song > > The try_to_unmap_one() function currently handles PMD-mapped THPs > inefficiently. It first splits the PMD into PTEs, copies the dirty > state from the PMD to the PTEs, iterates over the PTEs to locate > the dirty state, and then marks the THP as swap-backed. This process > involves unnecessary PMD splitting and redundant iteration. Instead, > this functionality can be efficiently managed in > __discard_anon_folio_pmd_locked(), avoiding the extra steps and > improving performance. > > The following microbenchmark redirties folios after invoking MADV_FREE, > then measures the time taken to perform memory reclamation (actually > set those folios swapbacked again) on the redirtied folios. > > #include > #include > #include > #include > > #define SIZE 128*1024*1024 // 128 MB > > 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); > /* redirty after MADV_FREE */ > memset((void *)p, 1, SIZE); > > clock_t start_time = clock(); > madvise((void *)p, SIZE, MADV_PAGEOUT); > clock_t end_time = clock(); > > double elapsed_time = (double)(end_time - start_time) / CLOCKS_PER_SEC; > printf("Time taken by reclamation: %f seconds\n", elapsed_time); > > munmap((void *)p, SIZE); > } > return 0; > } > > Testing results are as below, > w/o patch: > ~ # ./a.out > Time taken by reclamation: 0.007300 seconds > Time taken by reclamation: 0.007226 seconds > Time taken by reclamation: 0.007295 seconds > Time taken by reclamation: 0.007731 seconds > Time taken by reclamation: 0.007134 seconds > Time taken by reclamation: 0.007285 seconds > Time taken by reclamation: 0.007720 seconds > Time taken by reclamation: 0.007128 seconds > Time taken by reclamation: 0.007710 seconds > Time taken by reclamation: 0.007712 seconds > Time taken by reclamation: 0.007236 seconds > Time taken by reclamation: 0.007690 seconds > Time taken by reclamation: 0.007174 seconds > Time taken by reclamation: 0.007670 seconds > Time taken by reclamation: 0.007169 seconds > Time taken by reclamation: 0.007305 seconds > Time taken by reclamation: 0.007432 seconds > Time taken by reclamation: 0.007158 seconds > Time taken by reclamation: 0.007133 seconds > … > > w/ patch > > ~ # ./a.out > Time taken by reclamation: 0.002124 seconds > Time taken by reclamation: 0.002116 seconds > Time taken by reclamation: 0.002150 seconds > Time taken by reclamation: 0.002261 seconds > Time taken by reclamation: 0.002137 seconds > Time taken by reclamation: 0.002173 seconds > Time taken by reclamation: 0.002063 seconds > Time taken by reclamation: 0.002088 seconds > Time taken by reclamation: 0.002169 seconds > Time taken by reclamation: 0.002124 seconds > Time taken by reclamation: 0.002111 seconds > Time taken by reclamation: 0.002224 seconds > Time taken by reclamation: 0.002297 seconds > Time taken by reclamation: 0.002260 seconds > Time taken by reclamation: 0.002246 seconds > Time taken by reclamation: 0.002272 seconds > Time taken by reclamation: 0.002277 seconds > Time taken by reclamation: 0.002462 seconds Good result. > This patch significantly speeds up try_to_unmap_one() by allowing it > to skip redirtied THPs without splitting the PMD. > > Suggested-by: Baolin Wang > Suggested-by: Lance Yang > Signed-off-by: Barry Song LGTM. Reviewed-by: Baolin Wang