From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qe0-f45.google.com (mail-qe0-f45.google.com [209.85.128.45]) by kanga.kvack.org (Postfix) with ESMTP id BA6F76B0035 for ; Mon, 6 Jan 2014 21:21:06 -0500 (EST) Received: by mail-qe0-f45.google.com with SMTP id 6so18986649qea.4 for ; Mon, 06 Jan 2014 18:21:06 -0800 (PST) Received: from ozlabs.org (ozlabs.org. [2402:b800:7003:1:1::1]) by mx.google.com with ESMTPS id kc8si74137789qeb.27.2014.01.06.18.21.04 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 06 Jan 2014 18:21:05 -0800 (PST) Date: Tue, 7 Jan 2014 13:21:00 +1100 From: Anton Blanchard Subject: [PATCH] slub: Don't throw away partial remote slabs if there is no local memory Message-ID: <20140107132100.5b5ad198@kryten> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: benh@kernel.crashing.org, paulus@samba.org, cl@linux-foundation.org, penberg@kernel.org, mpm@selenic.com, nacc@linux.vnet.ibm.com Cc: linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org We noticed a huge amount of slab memory consumed on a large ppc64 box: Slab: 2094336 kB Almost 2GB. This box is not balanced and some nodes do not have local memory, causing slub to be very inefficient in its slab usage. Each time we call kmem_cache_alloc_node slub checks the per cpu slab, sees it isn't node local, deactivates it and tries to allocate a new slab. On empty nodes we will allocate a new remote slab and use the first slot, but as explained above when we get called a second time we will just deactivate that slab and retry. As such we end up only using 1 entry in each slab: slab mem objects used active ------------------------------------ kmalloc-16384 1404 MB 4.90% task_struct 668 MB 2.90% kmalloc-128 193 MB 3.61% kmalloc-192 152 MB 5.23% kmalloc-8192 72 MB 23.40% kmalloc-16 64 MB 7.43% kmalloc-512 33 MB 22.41% The patch below checks that a node is not empty before deactivating a slab and trying to allocate it again. With this patch applied we now use about 352MB: Slab: 360192 kB And our efficiency is much better: slab mem objects used active ------------------------------------ kmalloc-16384 92 MB 74.27% task_struct 23 MB 83.46% idr_layer_cache 18 MB 100.00% pgtable-2^12 17 MB 100.00% kmalloc-65536 15 MB 100.00% inode_cache 14 MB 100.00% kmalloc-256 14 MB 97.81% kmalloc-8192 14 MB 85.71% Signed-off-by: Anton Blanchard --- Thoughts? It seems like we could hit a similar situation if a machine is balanced but we run out of memory on a single node. Index: b/mm/slub.c =================================================================== --- a/mm/slub.c +++ b/mm/slub.c @@ -2278,10 +2278,17 @@ redo: if (unlikely(!node_match(page, node))) { stat(s, ALLOC_NODE_MISMATCH); - deactivate_slab(s, page, c->freelist); - c->page = NULL; - c->freelist = NULL; - goto new_slab; + + /* + * If the node contains no memory there is no point in trying + * to allocate a new node local slab + */ + if (node_spanned_pages(node)) { + deactivate_slab(s, page, c->freelist); + c->page = NULL; + c->freelist = NULL; + goto new_slab; + } } /* -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org