On 1/2/19 8:28 PM, Tetsuo Handa wrote: > On 2019/01/03 3:19, Qian Cai wrote: >> On 1/2/19 1:06 PM, Mel Gorman wrote: >> >>> While I recognise there is no test case available, how often does this >>> trigger in syzbot as it would be nice to have some confirmation any >>> patch is really fixing the problem. >> >> I think I did manage to trigger this every time running a mmap() workload >> causing swapping and a low-memory situation [1]. >> >> [1] >> https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/mem/oom/oom01.c > > wakeup_kswapd() is called because tlb_next_batch() is doing GFP_NOWAIT > allocation. But since tlb_next_batch() can tolerate allocation failure, > does below change in tlb_next_batch() help? > > #define GFP_NOWAIT (__GFP_KSWAPD_RECLAIM) > > - batch = (void *)__get_free_pages(GFP_NOWAIT | __GFP_NOWARN, 0); > + batch = (void *)__get_free_pages(__GFP_NOWARN, 0); No. In oom01 case, it is from, do_anonymous_page __alloc_zeroed_user_highpage alloc_page_vma(GFP_HIGHUSER ... GFP_HIGHUSER -> GFP_USER -> __GFP_RECLAIM -> ___GFP_KSWAPD_RECLAIM Then, it has this new code in steal_suitable_fallback() via 1c30844d2df (mm: reclaim small amounts of memory when an external fragmentation event occurs) /* * Boost watermarks to increase reclaim pressure to reduce * the likelihood of future fallbacks. Wake kswapd now as * the node may be balanced overall and kswapd will not * wake naturally. */ boost_watermark(zone); if (alloc_flags & ALLOC_KSWAPD) wakeup_kswapd(zone, 0, 0, zone_idx(zone));
