On Sat, May 31, 2014 at 03:04:58PM +0400, Vladimir Davydov wrote: > On Fri, May 30, 2014 at 09:57:10AM -0500, Christoph Lameter wrote: > > On Fri, 30 May 2014, Vladimir Davydov wrote: > > > > > (3) is a bit more difficult, because slabs are added to per-cpu partial > > > lists lock-less. Fortunately, we only have to handle the __slab_free > > > case, because, as there shouldn't be any allocation requests dispatched > > > to a dead memcg cache, get_partial_node() should never be called. In > > > __slab_free we use cmpxchg to modify kmem_cache_cpu->partial (see > > > put_cpu_partial) so that setting ->partial to a special value, which > > > will make put_cpu_partial bail out, will do the trick. > > > > > > Note, this shouldn't affect performance, because keeping empty slabs on > > > per node lists as well as using per cpu partials are only worthwhile if > > > the cache is used for allocations, which isn't the case for dead caches. > > > > This all sounds pretty good to me but we still have some pretty extensive > > modifications that I would rather avoid. > > > > In put_cpu_partial you can simply check that the memcg is dead right? This > > would avoid all the other modifications I would think and will not require > > a special value for the per cpu partial pointer. > > That would be racy. The check if memcg is dead and the write to per cpu > partial ptr wouldn't proceed as one atomic operation. If we set the dead > flag from another thread between these two operations, put_cpu_partial > will add a slab to a per cpu partial list *after* the cache was zapped. Hello, Vladimir. I think that we can do (3) easily. If we check memcg_cache_dead() in the end of put_cpu_partial() rather than in the begin of put_cpu_partial(), we can avoid the race you mentioned. If someone do put_cpu_partial() before dead flag is set, it can be zapped by who set dead flag. And if someone do put_cpu_partial() after dead flag is set, it can be zapped by who do put_cpu_partial(). Thanks. -- 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>