On Mon, Feb 22, 2021 at 06:31:12PM +0800, Muchun Song wrote: > On Mon, Feb 22, 2021 at 5:25 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > On Sat 20-02-21 12:20:36, Muchun Song wrote: > > > On Fri, Feb 19, 2021 at 10:12 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > [...] > > > > What about hugetlb page poisoning on HW failure (resp. soft offlining)? > > > > > > If the HW poisoned hugetlb page failed to be dissolved, the page > > > will go back to the free list with PG_HWPoison set. But the page > > > will not be used, because we will check whether the page is HW > > > poisoned when it is dequeued from the free list. If so, we will skip > > > this page. Not really. If the huge page is dissolved, we will take the page out of the the freelist. See take_page_off_buddy in memory_failure_hugetlb. In an ideal world, we should inspect that page in free_pages_prepare(), remove the HPWpoisoned page and process the others, without letting that page hit Buddy. And not only for hugetlb, but for any higher order page. See how memory_failure() happily disengage itself when it finds a higher order page. It does it because we have the premise that once that page hits Buddy, it will stay there as the check_new_page guards us. But this has been proofed to be quite a weak measure, as compaction does not performs such a check, and so the page can sneak in. I fixed that for soft-offline, and for memory-failure in some cases, but more needs to be done and is it in my TODO list. > > Can this lead to an under provisioned pool then? Or is there a new > > hugetlb allocated to replace the poisoned one? > > Actually, no page will be allocated. Your concern is right. But without > this patch, the result does not change. e.g. The HW poisoned page > can fail to be dissolved when h->free_huge_pages is equal to > h->resv_huge_pages. But no one seems to have reported this issue so > far. Maybe this behavior needs improvement in the feature. Yes, something to improve. I shall have a look. -- Oscar Salvador SUSE L3
