On Fri 18-10-19 13:00:45, David Hildenbrand wrote: > On 18.10.19 10:55, Michal Hocko wrote: > > On Fri 18-10-19 10:38:21, David Hildenbrand wrote: > > > On 18.10.19 10:24, Michal Hocko wrote: > > > > On Fri 18-10-19 10:13:36, David Hildenbrand wrote: > > > > [...] > > > > > However, if the compound page spans multiple pageblocks > > > > > > > > Although hugetlb pages spanning pageblocks are possible this shouldn't > > > > matter in__test_page_isolated_in_pageblock because this function doesn't > > > > really operate on pageblocks as the name suggests. It is simply > > > > traversing all valid RAM ranges (see walk_system_ram_range). > > > > > > As long as the hugepages don't span memory blocks/sections, you are right. I > > > have no experience with gigantic pages in this regard. > > > > They can clearly span sections (1GB is larger than 128MB). Why do you > > think it matters actually? walk_system_ram_range walks RAM ranges and no > > allocation should span holes in RAM right? > > > > Let's explore what I was thinking. If we can agree that any compound page is > always aligned to its size , then what I tell here is not applicable. I know > it is true for gigantic pages. > > Some extreme example to clarify > > [ memory block 0 (128MB) ][ memory block 1 (128MB) ] > [ compound page (128MB) ] > > If you would offline memory block 1, and you detect PG_offline on the first > page of that memory block (PageHWPoison(compound_head(page))), you would > jump over the whole memory block (pfn += 1 << compound_order(page)), leaving > 64MB of the memory block unchecked. > > Again, if any compound page has the alignment restrictions (PFN of head > aligned to 1 << compound_order(page)), this is not possible. > > > If it is, however, possible, the "clean" thing would be to only jump over > the remaining part of the compound page, e.g., something like > > pfn += (1 << compound_order(page)) - (page - compound_head(page))); OK, I see what you mean now. In other words similar to eeb0efd071d82. -- Michal Hocko SUSE Labs
