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AJvYcCVTv9MjC/3Ap/XH9C7jlZOpA2n7Fo2elXBKYE6Bb/NVXTBN2//nnspYezQndQNvuPuikJM6P/g0GA==@kvack.org X-Gm-Message-State: AOJu0YyGVhbUl1NRg17iHmlpUwZ/pn2ua/vyyd8IDyt6s6ynAGUeOkoU MHGiRA24zfLljBS/rmsyGegSoHG7A6g2P7gD3DKX9JY1bVYI/XJ2t0xF/E8NVBM= X-Google-Smtp-Source: AGHT+IFn9uKAYqxeIHcBhEtVAzeVdVtGgLCawnaOi087//SWtVli/uKCehKFYsPaoX8aH6BzIlqxLA== X-Received: by 2002:a05:6830:f8c:b0:713:ba39:641c with SMTP id 46e09a7af769-7181a5de231mr712381a34.6.1729233441232; Thu, 17 Oct 2024 23:37:21 -0700 (PDT) Received: from GQ6QX3JCW2.bytedance.net ([203.208.189.10]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-7eacc28b881sm638650a12.57.2024.10.17.23.37.16 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Thu, 17 Oct 2024 23:37:20 -0700 (PDT) From: lizhe.67@bytedance.com To: willy@infradead.org Cc: akpm@linux-foundation.org, boqun.feng@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lizhe.67@bytedance.com, longman@redhat.com, mingo@redhat.com, peterz@infradead.org, will@kernel.org Subject: Re: [RFC 2/2] khugepaged: use upgrade_read() to optimize collapse_huge_page Date: Fri, 18 Oct 2024 14:37:12 +0800 Message-ID: <20241018063712.44028-1-lizhe.67@bytedance.com> X-Mailer: git-send-email 2.45.2 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: BD3EC140002 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 18d7ccq5kss117pg59umoqzyckxjgeoq X-HE-Tag: 1729233434-356347 X-HE-Meta: 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 6fjDlIGp X9W3wg6MXu7WgzZgfeCBBg8hKl8yCB7UwSxl7r0ptENF+rbnAwbfQCFN0+xqqxJj7nXqj4uzNMJx1MZQ6RiDbN4UPfFdF5eJOWCHKnTy2qV0I7WcN527ItRYelYMs1rW7vJmcmzHvNPyO23zIPXh8/HMt4U/w7kzCOCMLtz8krhWss06yCOYuepCwZj9QkmVaFggJkGcav8AvUL8hCnQpPXT3yeh5CxFnc+PQZQasiUUmWfP2BHlVLlkvmt/cRhIbv+/ZcuHBpw3qzF+kfxP0MRiRVFHFywraPm6IECjsAbL1ZMMoRRTUsGon2wiSRjxsRc6WlrdPWrryP985tlkfy20g7N+OzqsVX9dlyFf/bNI+kyfUWEk1IOLiIFAtXDOu6vKu/3ao0c7Wk4SpFyYvzXoyItv09rOYgmMHr4siPIhL4oLfU/T6QAI9UfXiDSy4AMILph7AbYmXFBj5ZnTkhGf5IRT04GKyaTGyr2chBCuDmXs= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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 Thu, 17 Oct 2024 14:20:12 +0100, willy@infradead.org wrote: > On Thu, Oct 17, 2024 at 02:18:41PM +0800, lizhe.67@bytedance.com wrote: > > On Wed, 16 Oct 2024 12:53:15 +0100, willy@infradead.org wrote: > > > > >On Wed, Oct 16, 2024 at 12:36:00PM +0800, lizhe.67@bytedance.com wrote: > > >> From: Li Zhe > > >> > > >> In function collapse_huge_page(), we drop mmap read lock and get > > >> mmap write lock to prevent most accesses to pagetables. There is > > >> a small time window to allow other tasks to acquire the mmap lock. > > >> With the use of upgrade_read(), we don't need to check vma and pmd > > >> again in most cases. > > > > > >This is clearly a performance optimisation. So you must have some > > >numebrs that justify this, please include them. > > > > Yes, I will add the relevant data to v2 patch. > > How about telling us all now so we know whether to continue discussing > this? In my test environment, function collapse_huge_page() only achieved a 0.25% performance improvement. I use ftrace to get the execution time of collapse_huge_page(). The test code and test command are as follows. (1) Test result: average execution time of collapse_huge_page() before this patch: 1611.06283 us after this patch: 1597.01474 us (2) Test code: #define MMAP_SIZE (2ul*1024*1024) #define ALIGN(x, mask) (((x) + ((mask)-1)) & ~((mask)-1)) int main(void) { int num = 100; size_t page_sz = getpagesize(); while (num--) { size_t index; unsigned char *p_map; unsigned char *p_map_real; p_map = (unsigned char *)mmap(0, 2 * MMAP_SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE|MAP_ANON, -1, 0); if (p_map == MAP_FAILED) { printf("mmap fail\n"); return -1; } else { p_map_real = (char *)ALIGN((unsigned long)p_map, MMAP_SIZE); printf("mmap get %p, align to %p\n", p_map, p_map_real); } for(index = 0; index < MMAP_SIZE; index += page_sz) p_map_real[index] = 6; int ret = madvise(p_map_real, MMAP_SIZE, 25); printf("ret is %d\n", ret); munmap(p_map, 2 * MMAP_SIZE); } return 0; } (3) Test command: echo never > /sys/kernel/mm/transparent_hugepage/enabled gcc test.c -o test trace-cmd record -p function_graph -g collapse_huge_page --max-graph-depth 1 ./test The optimization of the function collapse_huge_page() seems insignificant. I am not sure whether it will have a more obvious optimization effect in other scenarios.