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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 44BE7140011 X-Rspam-User: X-Rspamd-Server: rspam06 X-Stat-Signature: wzs87ir99rorew59fbapbyg14arx3wjz X-HE-Tag: 1750769723-968034 X-HE-Meta: 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 S9aRMCHr Z2nFlWX1Naau2+RO6FGwQk9Y9jfogsohGesHn70yyRDO88NHR/EyPP3VPvcID2bcaLeo316oTed32o6XdZICNrjigg+D50FcwoV8X4VseoD9Un3hASDnX0ffQzVGaoH8wq9gPlyzAsUt6xquvQdNoEY0EYzZtVXCkHxUe/6aLU1b1ts8+dUEEzIuqlcyEQ2aTWvBZBJxQSEVOwpqbTv2X+8/JZ7tHYaxOEiAULgGyZV0RPN53/aOwJ1iyCyTeI5zqFRN5pv129ciLb9qUDxajHQLc5qKi9kKanAhXhU+BHoch2suTwb8DbQMafl7MueLguEz+6mXe52UZauU2eDqoOzQ+pHuNiobbuYByXLfrWbC9rigTAhXVFs7gLZFa78Z/pTwSKZm46umtB46tOfORF9gftoWLdiPTsftNVSUcm+rfACTvByVxDR06iL09sWfZSesD703/G6SOd7kaBscnJm31ZVwRA6bmkcQSGbyrXoRdPvg= 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 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