From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx158.postini.com [74.125.245.158]) by kanga.kvack.org (Postfix) with SMTP id 9E8C16B0007 for ; Mon, 28 Jan 2013 21:03:13 -0500 (EST) Received: by mail-pa0-f50.google.com with SMTP id hz10so60390pad.23 for ; Mon, 28 Jan 2013 18:03:12 -0800 (PST) Date: Mon, 28 Jan 2013 18:03:16 -0800 (PST) From: Hugh Dickins Subject: Re: [PATCH 6/11] ksm: remove old stable nodes more thoroughly In-Reply-To: <20130128154407.16a623a4.akpm@linux-foundation.org> Message-ID: References: <20130128154407.16a623a4.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Petr Holasek , Andrea Arcangeli , Izik Eidus , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Mon, 28 Jan 2013, Andrew Morton wrote: > On Fri, 25 Jan 2013 18:01:59 -0800 (PST) > Hugh Dickins wrote: > > > +static int remove_all_stable_nodes(void) > > +{ > > + struct stable_node *stable_node; > > + int nid; > > + int err = 0; > > + > > + for (nid = 0; nid < nr_node_ids; nid++) { > > + while (root_stable_tree[nid].rb_node) { > > + stable_node = rb_entry(root_stable_tree[nid].rb_node, > > + struct stable_node, node); > > + if (remove_stable_node(stable_node)) { > > + err = -EBUSY; > > It's a bit rude to overwrite remove_stable_node()'s return value. Well.... yes, but only the tiniest bit rude :) > > > + break; /* proceed to next nid */ > > + } > > + cond_resched(); > > Why is this here? Because we don't have a limit on the length of this loop, and if every node which remove_stable_node() finds is already stale, and has no rmap_item still attached, then there would be no rescheduling point in the unbounded loop without this one. I was taught to worry about bad latencies even in unpreemptible kernels. Hugh -- 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