On Thu 11-03-21 14:34:04, Muchun Song wrote: > On Wed, Mar 10, 2021 at 11:28 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > On Mon 08-03-21 18:28:03, Muchun Song wrote: > > > Because we reuse the first tail vmemmap page frame and remap it > > > with read-only, we cannot set the PageHWPosion on some tail pages. > > > So we can use the head[4].private (There are at least 128 struct > > > page structures associated with the optimized HugeTLB page, so > > > using head[4].private is safe) to record the real error page index > > > and set the raw error page PageHWPoison later. > > > > Can we have more poisoned tail pages? Also who does consume that index > > and set the HWPoison on the proper tail page? > > Good point. I look at the routine of memory failure closely. > If we do not clear the HWPoison of the head page, we cannot > poison another tail page. > > So we should not set the destructor of the huge page from > HUGETLB_PAGE_DTOR to NULL_COMPOUND_DTOR > before calling alloc_huge_page_vmemmap(). In this case, > the below check of PageHuge() always returns true. > > I need to fix this in the previous patch. > > memory_failure() > if (PageHuge(page)) > memory_failure_hugetlb() > head = compound_head(page) > if (TestSetPageHWPoison(head)) > return I have to say that I am not fully familiar with hwpoisoning code (especially after recent changes) but IIRC it does rely on hugetlb page dissolving. With the new code this operation can fail which is a new situation. Unless I am misunderstanding this can lead to a lost memory failure operation on other tail pages. Anyway the above answers the question why a single slot is sufficient so it would be great to mention that in a changelog along with the caveat that some pages might miss their poisoning. -- Michal Hocko SUSE Labs
