On Tue, 8 Dec 2015 17:56:35 +0300 Vladimir Davydov <vdavydov@xxxxxxxxxxxxx> wrote: > On Tue, Dec 08, 2015 at 08:15:21AM -0600, Christoph Lameter wrote: > > On Tue, 8 Dec 2015, Vladimir Davydov wrote: > > > > > If producers are represented by different processes, they can belong to > > > different memory cgroups, so that objects passed to the consumer will > > > come from different kmem caches (per memcg caches), although they are > > > all of the same kind. This means, we must call cache_from_obj() on each > > > object passed to kmem_cache_free_bulk() in order to free each object to > > > the cache it was allocated from. > > > > The we should change the API so that we do not specify kmem_cache on bulk > > free. Do it like kfree without any cache spec. > > > > Don't think so, because AFAIU the whole kmem_cache_free_bulk > optimization comes from the assumption that objects passed to it are > likely to share the same slab page. So they must be of the same kind, > otherwise no optimization would be possible and the function wouldn't > perform any better than calling kfree directly in a for-loop. By > requiring the caller to specify the cache we emphasize this. I agree with Vladimir here. The performance gain for SLUB is especially depended on that objects are likely to share the same slab page. It might not hurt SLAB as much. > Enabling kmemcg might break the assumption and neglect the benefit of > using kmem_cache_free_bulk, but it is to be expected, because kmem > accounting does not come for free. Callers who do care about the > performance and count every cpu cycle will surely disable it, in which > case cache_from_obj() will be a no-op and kmem_cache_free_bulk will bear > fruit. True, compiler does realize, when CONFIG_MEMCG_KMEM is disabled, that it can optimize the call to cache_from_obj() away. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat Author of http://www.iptv-analyzer.org LinkedIn: http://www.linkedin.com/in/brouer -- 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>