On Thu, Oct 7, 2021 at 11:19 AM Yang Shi <shy828301@xxxxxxxxx> wrote: > > On Thu, Oct 7, 2021 at 9:06 AM Peter Xu <peterx@xxxxxxxxxx> wrote: > > > > On Wed, Oct 06, 2021 at 04:57:38PM -0700, Yang Shi wrote: > > > > For example, I see that both unpoison_memory() and soft_offline_page() will > > > > call it too, does it mean that we'll also set the bits e.g. even when we want > > > > to inject an unpoison event too? > > > > > > unpoison_memory() should be not a problem since it will just bail out > > > once THP is met as the comment says: > > > > > > /* > > > * unpoison_memory() can encounter thp only when the thp is being > > > * worked by memory_failure() and the page lock is not held yet. > > > * In such case, we yield to memory_failure() and make unpoison fail. > > > */ > > > > But I still think setting the subpage-hwpoison bit hides too deep there, it'll > > be great we can keep get_hwpoison_page() as simple as a safe version of getting > > the refcount of the page we want. Or we'd still better touch up the comment > > above get_hwpoison_page() to show that side effect. > > > > > > > > > > > And I think we should set the flag for soft offline too, right? The > > > > I'm not familiar with either memory failure or soft offline, so far it looks > > right to me. However.. > > > > > soft offline does set the hwpoison flag for the corrupted sub page and > > > doesn't split file THP, > > > > .. I believe this will become not true after your patch 5, right? > > But THP split may fail, right? > > > > > > so it should be captured by page fault as well. And yes for poison injection. > > > > One more thing: besides thp split and page free, do we need to conditionally > > drop the HasHwpoisoned bit when received an unpoison event? > > It seems not to me, as the above comment from unpoison_memory() says > unpoison can encounter thp only when the thp is being worked by > memory_failure() and the page lock is not held yet. So it just bails > out. > > In addition, unpoison just works for software injected errors, not > real hardware failure. > > > > > If my understanding is correct, we may need to scan all the subpages there, to > > make sure HasHwpoisoned bit reflects the latest status for the thp in question. > > > > > > > > But your comment reminds me that get_hwpoison_page() is just called > > > when !MF_COUNT_INCREASED, so it means MADV_HWPOISON still could > > > escape. This needs to be covered too. > > > > Right, maybe that's also a clue that we shouldn't set the new page flag within > > get_hwpoison_page(), since get_hwpoison_page() is actually well coupled with > > MF_COUNT_INCREASED and all of them are only about refcounting of the pages. > > Yeah, maybe, as long as there is not early bail out in some error > handling paths. It seems fine to move setting the flag out of get_hwpoison_page() to right before splitting THP so that both MF_COUNT_INCREASED and !MF_COUNT_INCREASED could be covered. > > > > > -- > > Peter Xu > >
