Messages in this thread | | | Subject | Re: [PATCH] mm: thp: fix potential clearing to referenced flag in page_idle_clear_pte_refs_one() | From | Yang Shi <> | Date | Thu, 8 Feb 2018 20:47:35 -0800 |
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On 2/8/18 8:33 PM, Kirill A. Shutemov wrote: > On Thu, Feb 08, 2018 at 02:39:26PM -0800, Andrew Morton wrote: >> On Tue, 6 Feb 2018 08:06:36 +0800 Yang Shi <yang.shi@linux.alibaba.com> wrote: >> >>> For PTE-mapped THP, the compound THP has not been split to normal 4K >>> pages yet, the whole THP is considered referenced if any one of sub >>> page is referenced. >>> >>> When walking PTE-mapped THP by pvmw, all relevant PTEs will be checked >>> to retrieve referenced bit. But, the current code just returns the >>> result of the last PTE. If the last PTE has not referenced, the >>> referenced flag will be cleared. >>> >>> So, here just break pvmw walk once referenced PTE is found if the page >>> is a part of THP. >>> >>> ... >>> >>> --- a/mm/page_idle.c >>> +++ b/mm/page_idle.c >>> @@ -67,6 +67,14 @@ static bool page_idle_clear_pte_refs_one(struct page *page, >>> if (pvmw.pte) { >>> referenced = ptep_clear_young_notify(vma, addr, >>> pvmw.pte); >>> + /* >>> + * For PTE-mapped THP, one sub page is referenced, >>> + * the whole THP is referenced. >>> + */ >>> + if (referenced && PageTransCompound(pvmw.page)) { >>> + page_vma_mapped_walk_done(&pvmw); >>> + break; >>> + } >> This means that the function will no longer clear the referenced bits >> in all the ptes. What effect does this have and should we document >> this in some fashion? > Yeah, the patch is wrong. We need to get all ptes for THP cleared. > > What about something like this instead (untested):
Thanks, Kirill. It looks correct. All ptes should be cleared.
I'm going to prepare v2 patch.
Regards, Yang
> > diff --git a/mm/page_idle.c b/mm/page_idle.c > index 0a49374e6931..6876522c9dce 100644 > --- a/mm/page_idle.c > +++ b/mm/page_idle.c > @@ -65,10 +65,10 @@ static bool page_idle_clear_pte_refs_one(struct page *page, > while (page_vma_mapped_walk(&pvmw)) { > addr = pvmw.address; > if (pvmw.pte) { > - referenced = ptep_clear_young_notify(vma, addr, > + referenced |= ptep_clear_young_notify(vma, addr, > pvmw.pte); > } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) { > - referenced = pmdp_clear_young_notify(vma, addr, > + referenced |= pmdp_clear_young_notify(vma, addr, > pvmw.pmd); > } else { > /* unexpected pmd-mapped page? */
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