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 | Fri, 9 Feb 2018 11:14:29 -0800 |
| |
On 2/9/18 12:16 AM, Kirill A. Shutemov wrote: > On Thu, Feb 08, 2018 at 08:47:35PM -0800, Yang Shi wrote: >> >> 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. > Note, it should be ||=, not |= (although it would work correctly too).
checkpatch doesn't like "||=", it reports no space error. Use referenced = referenced || ptep_clear_young_notify(...) to make checkpatch happy.
Regards, Yang
> > I should really wake up properly before touching code. :-/ >
| |