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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 10 Apr 2025, at 6:29, Barry Song wrote: > On Thu, Apr 10, 2025 at 9:05=E2=80=AFPM Baolin Wang > wrote: >> >> >> >> On 2025/4/10 16:14, Barry Song wrote: >>> On Wed, Apr 9, 2025 at 1:16=E2=80=AFAM Baolin Wang >>> wrote: >>>> >>>> When investigating performance issues during file folio unmap, I notic= ed some >>>> behavioral differences in handling non-PMD-sized folios and PMD-sized = folios. >>>> For non-PMD-sized file folios, it will call folio_mark_accessed() to m= ark the >>>> folio as having seen activity, but this is not done for PMD-sized foli= os. >>>> >>>> This might not cause obvious issues, but a potential problem could be = that, >>>> it might lead to more frequent refaults of PMD-sized file folios under= memory >>>> pressure. Therefore, I am unsure whether the folio_mark_accessed() sho= uld be >>>> added for PMD-sized file folios? >>>> >>>> Signed-off-by: Baolin Wang >>>> --- >>>> mm/huge_memory.c | 4 ++++ >>>> 1 file changed, 4 insertions(+) >>>> >>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>>> index 6ac6d468af0d..b3ade7ac5bbf 100644 >>>> --- a/mm/huge_memory.c >>>> +++ b/mm/huge_memory.c >>>> @@ -2262,6 +2262,10 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct= vm_area_struct *vma, >>>> zap_deposited_table(tlb->mm, pmd); >>>> add_mm_counter(tlb->mm, mm_counter_file(folio= ), >>>> -HPAGE_PMD_NR); >>>> + >>>> + if (flush_needed && pmd_young(orig_pmd) && >>>> + likely(vma_has_recency(vma))) >>>> + folio_mark_accessed(folio); >>> >>> Acked-by: Barry Song >> >> Thanks. >> >>> I also came across an interesting observation: on a memory-limited syst= em, >>> demoting unmapped file folios in the LRU=E2=80=94specifically when thei= r mapcount >>> drops from 1 to 0=E2=80=94can actually improve performance. >> >> These file folios are used only once? Can folio_set_dropbehind() be used >> to optimize it, which can avoid the LRU activity movement in >> folio_mark_accessed()? > > For instance, when a process, such as a game, just exits, it can be expec= ted > that it won't be used again in the near future. As a result, demoting > its previously > unmapped file pages can improve performance. Is it possible to mark the dying VMAs either VM_SEQ_READ or VM_RAND_READ so that folio_mark_accessed() will be skipped? Or a new vm_flag? Will it work? > > Of course, for file folios mapped by multiple processes, such as > common .so files, > it's a different story. Typically, their mapcounts are always high. Text VMAs should not be marked. > >> >>> If others have observed the same behavior, we might not need to mark th= em >>> as accessed in that scenario. >>> >>>> } >>>> >>>> spin_unlock(ptl); >>>> -- >>>> 2.43.5 >>>> >>> > > Thanks > Barry Best Regards, Yan, Zi