Hey Barry, Thanks for taking time to review! On Mon, Feb 26, 2024 at 12:00 PM Barry Song <21cnbao@xxxxxxxxx> wrote: [...] > On Mon, Feb 26, 2024 at 1:33 AM Lance Yang <ioworker0@xxxxxxxxx> wrote: [...] > We did something similar on MADV_PAGEOUT[1] > [1] https://lore.kernel.org/linux-mm/20240118111036.72641-7-21cnbao@xxxxxxxxx/ Thanks for providing the link above. [...] > > + * Avoid unnecessary folio splitting if the large > > + * folio is entirely within the given range. > > + */ > > + folio_test_clear_dirty(folio); > > + folio_unlock(folio); > > + for (; addr != next_addr; pte++, addr += PAGE_SIZE) { > > + ptent = ptep_get(pte); > > + if (pte_young(ptent) || pte_dirty(ptent)) { > > + ptent = ptep_get_and_clear_full( > > + mm, addr, pte, tlb->fullmm); > > + ptent = pte_mkold(ptent); > > + ptent = pte_mkclean(ptent); > > + set_pte_at(mm, addr, pte, ptent); > > + tlb_remove_tlb_entry(tlb, pte, addr); > > + } > > The code works under the assumption the large folio is entirely mapped > in all PTEs in the range. This is not always true. > > This won't work in some cases as some PTEs might be mapping to the > large folios. some others might have been unmapped or mapped > to different folios. > > so in MADV_PAGEOUT, we have a function to check the folio is > really entirely mapped: > > +static inline bool pte_range_cont_mapped(unsigned long start_pfn, > + pte_t *start_pte, unsigned long start_addr, int nr) > +{ > + int i; > + pte_t pte_val; > + > + for (i = 0; i < nr; i++) { > + pte_val = ptep_get(start_pte + i); > + > + if (pte_none(pte_val)) > + return false; > + > + if (pte_pfn(pte_val) != (start_pfn + i)) > + return false; > + } > + > + return true; > +} Thanks for providing the information; it's very helpful to me! I made some changes. Would you mind taking another look, please? As a diff against this patch. diff --git a/mm/madvise.c b/mm/madvise.c index bcbf56595a2e..255d2f329be4 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -616,6 +616,18 @@ static long madvise_pageout(struct vm_area_struct *vma, return 0; } +static inline bool pte_range_cont_mapped(pte_t *pte, unsigned long nr) +{ + pte_t pte_val; + unsigned long pfn = pte_pfn(pte); + for (int i = 0; i < nr; i++) { + pte_val = ptep_get(pte + i); + if (pte_none(pte_val) || pte_pfn(pte_val) != (pfn + i)) + return false; + } + return true; +} + static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, struct mm_walk *walk) @@ -676,20 +688,25 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, */ if (folio_test_large(folio)) { int err; - unsigned long next_addr, align; + unsigned long nr, next_addr, align; if (folio_estimated_sharers(folio) != 1 || !folio_trylock(folio)) goto skip_large_folio; - align = folio_nr_pages(folio) * PAGE_SIZE; + nr = folio_nr_pages(folio); + align = nr * PAGE_SIZE; next_addr = ALIGN_DOWN(addr + align, align); /* - * If we mark only the subpages as lazyfree, - * split the large folio. + * If we mark only the subpages as lazyfree, or + * if there is a cow folio associated with this folio, + * or if this folio is not really entirely mapped, + * then split the large folio. */ - if (next_addr > end || next_addr - addr != align) + if (next_addr > end || next_addr - addr != align || + folio_total_mapcount(folio) != nr || + pte_range_cont_mapped(pte, nr)) goto split_large_folio; /* --- Thanks again for your time! Best, Lance
