On 12/28/2015 03:13 PM, Tetsuo Handa wrote: > Tetsuo Handa wrote: >> Tetsuo Handa wrote: >> > I got OOM killers while running heavy disk I/O (extracting kernel source, >> > running lxr's genxref command). (Environ: 4 CPUs / 2048MB RAM / no swap / XFS) >> > Do you think these OOM killers reasonable? Too weak against fragmentation? >> >> Since I cannot establish workload that caused December 24's natural OOM >> killers, I used the following stressor for generating similar situation. >> > > I came to feel that I am observing a different problem which is currently > hidden behind the "too small to fail" memory-allocation rule. That is, tasks > requesting order > 0 pages are continuously losing the competition when > tasks requesting order = 0 pages dominate, for reclaimed pages are stolen > by tasks requesting order = 0 pages before reclaimed pages are combined to > order > 0 pages (or maybe order > 0 pages are immediately split into > order = 0 pages due to tasks requesting order = 0 pages). Hm I would expect that as long as there are some reserves left that your reproducer cannot grab, there are some free pages left and the allocator should thus preserve the order-2 pages that combine, since order-0 allocations will get existing order-0 pages before splitting higher orders. Compaction should also be able to successfully combine order-2 without racing allocators thanks to per-cpu caching (but I'd have to check). So I think the problem is not higher-order page itself, but that order-2 needs 4 pages and thus needs to pass a bit higher watermark, thus being at disadvantage to order-0 allocations. Thus I would expect the order-2 pages to be there, but not available for allocation due to watermarks. > Currently, order <= PAGE_ALLOC_COSTLY_ORDER allocations implicitly retry > unless chosen by the OOM killer. Therefore, even if tasks requesting > order = 2 pages lost the competition when there are tasks requesting > order = 0 pages, the order = 2 allocation request is implicitly retried > and therefore the OOM killer is not invoked (though there is a problem that > tasks requesting order > 0 allocation will stall as long as tasks requesting > order = 0 pages dominate). > > But this patchset introduced a limit of 16 retries. Thus, if tasks requesting > order = 2 pages lost the competition for 16 times due to tasks requesting > order = 0 pages, tasks requesting order = 2 pages invoke the OOM killer. > To avoid the OOM killer, we need to make sure that pages reclaimed for > order > 0 allocations will not be stolen by tasks requesting order = 0 > allocations. > > Is my feeling plausible? > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>