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U2FsdGVkX19HZuWPRZc6ek1t+IF/YR/e8k0LTRkjM1dh+JOrvVHtjuIZGrvzm5VAL9yKH91aBE1x7/25vgBLTkP6FIObAgkRNwmb/aWi4WiPssGE2MvlkXGYxfiL1Z6jP4Tsf2pn2DPY4MvcbZmIrrimkG8NfPJLFPRrY/Fa+fZJ4ofhlLdbcYubyiyR9iggD6ifW/yJzkn6UAu8scnFEUlfhXtrtucjPw37JWS3gdbrEhj+wEd318/nLvRta2wbPwmKRfDJkVRoqVga9PH/vu46jpqAlE7JvL0kHodGH0RY+Hf93cjpKwr1yye7Y2AfC0yvE3nDMEF9HDiKSR0iV7e8Dl+/pnD4Of7otUnSanX1eWoUK9vhfqEmamnasZ17McQv2wE6fz5TPh18+aL35KX8ro8p0XmMxKrwNm+UzeoQXGqTBS8acdKADlfIIFBjTTtzSi2UqUNQcApsUWdBEr2/D7BdGgWCS2nm0Xy8Cac8AIvQ4wwD1dydqF/2zL4rMdXfcNBGo7HeQtJAtH02ejdljfZuBpNMNmnr7ocW4v41TtKTc97p4EicGIUmmDg0zNbb8UswYn52X3OniueH0b3zDVnLjsmNmYOqABo9wAJfRgVFDGfCI21tN4VG5za0UhFUEfz/XMAWVrKftFM9h/MU8vsSgMg5cMvB53HGBjpymk2Nj7c5V47GFu7T3uJd6srFG5Xm+WEQ5WuTmNn7+fsBczUI0PSEgbv4sLvvsEed5yBgafWtoQ7RpYx9avQ/uIyNsFNwAbKNqa2o7nSFKkBVNuwxUmnTutYXHiTkEji1vSvRbhFQNqFFDfGFs7R610fqRLFnFyx6+gAwOULfn23XV98lWL763/yu3VH4n0oCZgn1wW2StBCZPtvmHPD1CmX6BhvFDe9YYv5nfl6ts5s0IWzNdiUbeTEP4iJElmnzkC98gKX19u2rqABIpyZclxFMWQMxsEX3TofMgQg mWAiYy7D 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Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ] > > On Wed, Jul 10, 2024 at 4:04 PM David Hildenbrand wrote: >> On 10.07.24 06:02, Barry Song wrote: >>> On Wed, Jul 10, 2024 at 3:59 PM David Hildenbrand wrote: >>>> 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()? >>> my point is that the purpose is skipping redundant swap-out, if shmem is single >>> mapped, they could be also skipped. >> But they won't get necessarily *freed* when unmapping them. They might >> just continue living in tmpfs? where some other process might just map >> them later? >> > You're correct. I overlooked this aspect, focusing on swap and thinking of shmem > solely in terms of swap. > >> IMHO, there is a big difference here between anon and shmem. (well, >> anon_shmem would actually be different :) ) > Even though anon_shmem behaves similarly to anonymous memory when > releasing memory, it doesn't seem worth the added complexity? > > So unfortunately it seems Zhiguo still needs v10 to take folio_test_anon() > back? Sorry for my bad, Zhiguo. If folio_test_anon(folio) && folio_test_swapbacked(folio) condition is used, can it means that the folio is anonymous anther than shmem definitely? So does folio_likely_mapped_shared() need to be removed? > >> -- >> Cheers, >> >> David / dhildenb >> > Thanks > Barry Thanks Zhiguo