On Mon, Oct 21, 2024 at 2:13 AM Michal Hocko <mhocko@xxxxxxxx> wrote: > > On Sat 19-10-24 23:13:15, Yu Zhao wrote: > > OOM kills due to vastly overestimated free highatomic reserves were > > observed: > > > > ... invoked oom-killer: gfp_mask=0x100cca(GFP_HIGHUSER_MOVABLE), order=0 ... > > Node 0 Normal free:1482936kB boost:0kB min:410416kB low:739404kB high:1068392kB reserved_highatomic:1073152KB ... > > Node 0 Normal: 1292*4kB (ME) 1920*8kB (E) 383*16kB (UE) 220*32kB (ME) 340*64kB (E) 2155*128kB (UE) 3243*256kB (UE) 615*512kB (U) 1*1024kB (M) 0*2048kB 0*4096kB = 1477408kB > > > > The second line above shows that the OOM kill was due to the following > > condition: > > > > free (1482936kB) - reserved_highatomic (1073152kB) = 409784KB < min (410416kB) > > > > And the third line shows there were no free pages in any > > MIGRATE_HIGHATOMIC pageblocks, which otherwise would show up as type > > 'H'. Therefore __zone_watermark_unusable_free() overestimated free > > highatomic reserves. IOW, it underestimated the usable free memory by > > over 1GB, which resulted in the unnecessary OOM kill. > > Why doesn't unreserve_highatomic_pageblock deal with this situation? The current behavior of unreserve_highatomic_pageblock() seems WAI to me: it unreserves highatomic pageblocks that contain *free* pages so that those pages can become usable to others. There is nothing to unreserve when they have no free pages.
