On Mon, Oct 03, 2016 at 02:06:42PM +0200, Michal Hocko wrote: > On Sat 01-10-16 16:56:47, Vladimir Davydov wrote: > > Creating a lot of cgroups at the same time might stall all worker > > threads with kmem cache creation works, because kmem cache creation is > > done with the slab_mutex held. To prevent that from happening, let's use > > a special workqueue for kmem cache creation with max in-flight work > > items equal to 1. > > > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=172981 > > This looks like a regression but I am not really sure I understand what > has caused it. We had the WQ based cache creation since kmem was > introduced more or less. So is it 801faf0db894 ("mm/slab: lockless > decision to grow cache") which was pointed by bisection that changed the > timing resp. relaxed the cache creation to the point that would allow > this runaway? It is in case of SLAB. For SLUB the issue was caused by commit 81ae6d03952c ("mm/slub.c: replace kick_all_cpus_sync() with synchronize_sched() in kmem_cache_shrink()"). > This would be really useful for the stable backport > consideration. > > Also, if I understand the fix correctly, now we do limit the number of > workers to 1 thread. Is this really what we want? Wouldn't it be > possible that few memcgs could starve others fromm having their cache > created? What would be the result, missed charges? Now kmem caches are created in FIFO order, i.e. if one memcg called kmem_cache_alloc on a non-existent cache before another, it will be served first. Since the number of caches that can be created by a single memcg is obviously limited, I don't see any possibility of starvation. Actually, this patch doesn't introduce any functional changes regarding the order in which kmem caches are created, as the work function holds the global slab_mutex during its whole runtime anyway. We only avoid creating a thread per each work by making the queue single-threaded. -- 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>