On 2022/4/12 13:59, HORIGUCHI NAOYA(堀口 直也) wrote: > On Tue, Apr 12, 2022 at 10:47:53AM +0800, Miaohe Lin wrote: >> On 2022/4/11 21:13, HORIGUCHI NAOYA(堀口 直也) wrote: >>> Hi Miaohe, >>> >>> On Thu, Apr 07, 2022 at 09:03:52PM +0800, Miaohe Lin wrote: >>>> If me_huge_page meets a truncated huge page, hpage won't be dissolved >>> >>> I might not understand correctly what "truncated huge page" means. If it >>> means the page passed to me_huge_page() and truncate_error_page() is called >>> on it, the else branch you're trying to update is not chosen, so maybe it >>> sounds irrelevant to me? Could you elaborate it or share the procedure to >>> reproduce the case you care about? >> >> Sorry for making confusing. What 'truncated hugetlb page' means is that a hugepage is >> truncated but still on the way to free. So HPageMigratable is still set and we might >> come across it here. Does this make sense for you? > > Yes, it does. Thank you. > >> >>> >>>> even if we hold the last refcnt. It's because the truncated huge page >>>> has NULL page_mapping while it's not anonymous page too. Thus we lose >>>> the last chance to dissolve it into buddy to save healthy subpages. >>>> Remove PageAnon check to handle these huge pages too. >>>> >>>> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> >>>> --- >>>> mm/memory-failure.c | 3 +-- >>>> 1 file changed, 1 insertion(+), 2 deletions(-) >>>> >>>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c >>>> index bd563f47630c..3f054dbb169d 100644 >>>> --- a/mm/memory-failure.c >>>> +++ b/mm/memory-failure.c >>>> @@ -1046,8 +1046,7 @@ static int me_huge_page(struct page_state *ps, struct page *p) >>>> * hugepage, so we can free and dissolve it into buddy to >>>> * save healthy subpages. >>>> */ >>>> - if (PageAnon(hpage)) >>>> - put_page(hpage); >>> >>> I think that the reason of this "if (PageAnon(hpage))" is to not remove >>> hugepages for hugetlbfs files. Unlike anonymous hugepage, it can be >>> accessed from file after error handling, so we can't simply dissolve it >>> because otherwise another process reading the hugepage sees zeroed one >>> without knowing the memory error. >> >> In this branch, we have precondition that page_mapping is NULL. So it can't be hugepages >> for hugetlbfs files. It should be anonymous hugepages in most cases. If it's not anonymous >> hugepages too, i.e. (!page_mapping(hpage) && !PageAnon(hpage)), it could be free hugepages >> or 'truncated hugetlb page'. But we have already handled the free hugepages case, it should >> be 'truncated hugetlb page' here. Since it's on the way to free, we should put the refcnt >> to increase the chance that we can free and dissolve it into buddy to save healthy subpages. >> Or am I miss something? > > No, it sounds correct. So I agree with removing the "if". Could you also > update the inline comment just above it in the next version? We no longer > need to limitedly mention "anonymous hugepage". Sure. Will do it in next version. Many thanks! > > Thanks, > Naoya Horiguchi >
