[CC David] On Wed 13-07-16 22:19:23, Tetsuo Handa wrote: > >> On Mon 11-07-16 11:43:02, Mikulas Patocka wrote: > >> [...] > >>> The general problem is that the memory allocator does 16 retries to > >>> allocate a page and then triggers the OOM killer (and it doesn't take into > >>> account how much swap space is free or how many dirty pages were really > >>> swapped out while it waited). > >> > >> Well, that is not how it works exactly. We retry as long as there is a > >> reclaim progress (at least one page freed) back off only if the > >> reclaimable memory can exceed watermks which is scaled down in 16 > >> retries. The overal size of free swap is not really that important if we > >> cannot swap out like here due to complete memory reserves depletion: > >> https://okozina.fedorapeople.org/bugs/swap_on_dmcrypt/vmlog-1462458369-00000/sample-00011/dmesg: > >> [ 90.491276] Node 0 DMA free:0kB min:60kB low:72kB high:84kB active_anon:4096kB inactive_anon:4636kB active_file:212kB inactive_file:280kB unevictable:488kB isolated(anon):0kB isolated(file):0kB present:15992kB managed:15908kB mlocked:488kB dirty:276kB writeback:4636kB mapped:476kB shmem:12kB slab_reclaimable:204kB slab_unreclaimable:4700kB kernel_stack:48kB pagetables:120kB unstable:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:61132 all_unreclaimable? yes > >> [ 90.491283] lowmem_reserve[]: 0 977 977 977 > >> [ 90.491286] Node 0 DMA32 free:0kB min:3828kB low:4824kB high:5820kB active_anon:423820kB inactive_anon:424916kB active_file:17996kB inactive_file:21800kB unevictable:20724kB isolated(anon):384kB isolated(file):0kB present:1032184kB managed:1001260kB mlocked:20724kB dirty:25236kB writeback:49972kB mapped:23076kB shmem:1364kB slab_reclaimable:13796kB slab_unreclaimable:43008kB kernel_stack:2816kB pagetables:7320kB unstable:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:5635400 all_unreclaimable? yes > >> > >> Look at the amount of free memory. It is completely depleted. So it > >> smells like a process which has access to memory reserves has consumed > >> all of it. I suspect a __GFP_MEMALLOC resp. PF_MEMALLOC from softirq > >> context user which went off the leash. > > > > It is caused by the commit f9054c70d28bc214b2857cf8db8269f4f45a5e23. Prior > > to this commit, mempool allocations set __GFP_NOMEMALLOC, so they never > > exhausted reserved memory. With this commit, mempool allocations drop > > __GFP_NOMEMALLOC, so they can dig deeper (if the process has PF_MEMALLOC, > > they can bypass all limits). > > I wonder whether commit f9054c70d28bc214 ("mm, mempool: only set > __GFP_NOMEMALLOC if there are free elements") is doing correct thing. > It says > > If an oom killed thread calls mempool_alloc(), it is possible that it'll > loop forever if there are no elements on the freelist since > __GFP_NOMEMALLOC prevents it from accessing needed memory reserves in > oom conditions. I haven't studied the patch very deeply so I might be missing something but from a quick look the patch does exactly what the above says. mempool_alloc used to inhibit ALLOC_NO_WATERMARKS by default. David has only changed that to allow ALLOC_NO_WATERMARKS if there are no objects in the pool and so we have no fallback for the default __GFP_NORETRY request. > but we can allow mempool_alloc(__GFP_NOMEMALLOC) requests to access > memory reserves via below change, can't we? Well, I do not see all the potential side effects of such a change but I believe it shouldn't be really necessary because we should eventually allow ALLOC_NO_WATERMARKS even from mempool_alloc. > The purpose of allowing > ALLOC_NO_WATERMARKS via TIF_MEMDIE is to make sure current allocation > request does not to loop forever inside the page allocator, isn't it? > Why we need to allow mempool_alloc(__GFP_NOMEMALLOC) requests to use > ALLOC_NO_WATERMARKS when TIF_MEMDIE is not set? > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 6903b69..e4e3700 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3439,14 +3439,14 @@ gfp_to_alloc_flags(gfp_t gfp_mask) > } else if (unlikely(rt_task(current)) && !in_interrupt()) > alloc_flags |= ALLOC_HARDER; > > - if (likely(!(gfp_mask & __GFP_NOMEMALLOC))) { > + if (!in_interrupt() && unlikely(test_thread_flag(TIF_MEMDIE))) > + alloc_flags |= ALLOC_NO_WATERMARKS; > + else if (likely(!(gfp_mask & __GFP_NOMEMALLOC))) { > if (gfp_mask & __GFP_MEMALLOC) > alloc_flags |= ALLOC_NO_WATERMARKS; > else if (in_serving_softirq() && (current->flags & PF_MEMALLOC)) > alloc_flags |= ALLOC_NO_WATERMARKS; > - else if (!in_interrupt() && > - ((current->flags & PF_MEMALLOC) || > - unlikely(test_thread_flag(TIF_MEMDIE)))) > + else if (!in_interrupt() && (current->flags & PF_MEMALLOC)) > alloc_flags |= ALLOC_NO_WATERMARKS; > } > #ifdef CONFIG_CMA > > -- > 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> -- Michal Hocko SUSE Labs -- 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>