On Mon, Oct 21, 2024 at 11:26 AM Michal Hocko <mhocko@xxxxxxxx> wrote: > > On Mon 21-10-24 11:10:50, Yu Zhao wrote: > > 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. > > I do not follow. How can you have reserved highatomic pages of that size > without having page blocks with free memory. Sorry I might still not get your question: are you saying it's not possible for 524 pageblocks (reserved_highatomic=1073152kB) not to have free pages? It might be uncommon but I don't think it's impossible. > In other words is this an > accounting problem or reserves problem? I don't follow here: why does it need to be one of the two? reserved_highatomic can go up to 1% of the zone, and all reserves can be used for highatomic allocs, leaving no free pages in reserved_highatomic.
