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Tue, 09 Jul 2024 20:59:03 -0700 (PDT) X-Google-Smtp-Source: AGHT+IH+WmChsw2kMnNV1Fky99vcI5Yo/GR8BmnMknPXKAx8NTttsHGVF2RDldwVYCl/YoQDSwl/ZQ== X-Received: by 2002:a05:6a21:918c:b0:1c0:defa:b68e with SMTP id adf61e73a8af0-1c2984ce0e7mr3689435637.39.1720583943109; Tue, 09 Jul 2024 20:59:03 -0700 (PDT) Received: from [172.20.2.228] ([4.28.11.157]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1fbb6ac0841sm23425215ad.211.2024.07.09.20.59.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 09 Jul 2024 20:59:02 -0700 (PDT) Message-ID: Date: Wed, 10 Jul 2024 05:59:01 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7] mm: shrink skip folio mapped by an exiting process To: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org Cc: baohua@kernel.org, justinjiang@vivo.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, opensource.kernel@vivo.com, willy@infradead.org References: <20240709142312.372b20d49c6a97ecd2cd9904@linux-foundation.org> <20240710033212.36497-1-21cnbao@gmail.com> Content-Language: en-US From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 10.07.24 05:32, Barry Song wrote: > On Wed, Jul 10, 2024 at 9:23 AM Andrew Morton wrote: >> >> On Tue,  9 Jul 2024 20:31:15 +0800 Zhiguo Jiang wrote: >> >>> The releasing process of the non-shared anonymous folio mapped solely by >>> an exiting process may go through two flows: 1) the anonymous folio is >>> firstly is swaped-out into swapspace and transformed into a swp_entry >>> in shrink_folio_list; 2) then the swp_entry is released in the process >>> exiting flow. This will result in the high cpu load of releasing a >>> non-shared anonymous folio mapped solely by an exiting process. >>> >>> When the low system memory and the exiting process exist at the same >>> time, it will be likely to happen, because the non-shared anonymous >>> folio mapped solely by an exiting process may be reclaimed by >>> shrink_folio_list. >>> >>> This patch is that shrink skips the non-shared anonymous folio solely >>> mapped by an exting process and this folio is only released directly in >>> the process exiting flow, which will save swap-out time and alleviate >>> the load of the process exiting. >> >> It would be helpful to provide some before-and-after runtime >> measurements, please.  It's a performance optimization so please let's >> see what effect it has. > > Hi Andrew, > > This was something I was curious about too, so I created a small test program > that allocates and continuously writes to 256MB of memory. Using QEMU, I set > up a small machine with only 300MB of RAM to trigger kswapd. > > qemu-system-aarch64 -M virt,gic-version=3,mte=off -nographic \ > -smp cpus=4 -cpu max \ > -m 300M -kernel arch/arm64/boot/Image > > The test program will be randomly terminated by its subprocess to trigger > the use case of this patch. > > #include > #include > #include > #include > #include > #include > #include > #include > > #define MEMORY_SIZE (256 * 1024 * 1024) > > unsigned char *memory; > > void allocate_and_write_memory() > { > memory = (unsigned char *)malloc(MEMORY_SIZE); > if (memory == NULL) { > perror("malloc"); > exit(EXIT_FAILURE); > } > > while (1) > memset(memory, 0x11, MEMORY_SIZE); > } > > int main() > { > pid_t pid; > srand(time(NULL)); > > pid = fork(); > > if (pid < 0) { > perror("fork"); > exit(EXIT_FAILURE); > } > > if (pid == 0) { > int delay = (rand() % 10000) + 10000; > usleep(delay * 1000); > > /* kill parent when it is busy on swapping */ > kill(getppid(), SIGKILL); > _exit(0); > } else { > allocate_and_write_memory(); > > wait(NULL); > > free(memory); > } > > return 0; > } > > I tracked the number of folios that could be redundantly > swapped out by adding a simple counter as shown below: > > @@ -879,6 +880,9 @@ static bool folio_referenced_one(struct folio *folio, > check_stable_address_space(vma->vm_mm)) && > folio_test_swapbacked(folio) && > !folio_likely_mapped_shared(folio)) { > + static long i, size; > + size += folio_size(folio); > + pr_err("index: %d skipped folio:%lx total size:%d\n", i++, (unsigned long)folio, size); > pra->referenced = -1; > page_vma_mapped_walk_done(&pvmw); > return false; > > > This is what I have observed: > > / # /home/barry/develop/linux/skip_swap_out_test > [ 82.925645] index: 0 skipped folio:fffffdffc0425400 total size:65536 > [ 82.925960] index: 1 skipped folio:fffffdffc0425800 total size:131072 > [ 82.927524] index: 2 skipped folio:fffffdffc0425c00 total size:196608 > [ 82.928649] index: 3 skipped folio:fffffdffc0426000 total size:262144 > [ 82.929383] index: 4 skipped folio:fffffdffc0426400 total size:327680 > [ 82.929995] index: 5 skipped folio:fffffdffc0426800 total size:393216 > ... > [ 88.469130] index: 6112 skipped folio:fffffdffc0390080 total size:97230848 > [ 88.469966] index: 6113 skipped folio:fffffdffc038d000 total size:97296384 > [ 89.023414] index: 6114 skipped folio:fffffdffc0366cc0 total size:97300480 > > I observed that this patch effectively skipped 6114 folios (either 4KB or 64KB > mTHP), potentially reducing the swap-out by up to 92MB (97,300,480 bytes) during > the process exit. > > Despite the numerous mistakes Zhiguo made in sending this patch, it is still > quite valuable. Please consider pulling his v9 into the mm tree for testing. BTW, we dropped the folio_test_anon() check, but what about shmem? They also do __folio_set_swapbacked()? -- Cheers, David / dhildenb