From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with SMTP id 8F2296B004F for ; Thu, 15 Oct 2009 19:04:16 -0400 (EDT) Date: Fri, 16 Oct 2009 00:04:14 +0100 (BST) From: Hugh Dickins Subject: Re: [PATCH 2/9] swap_info: change to array of pointers In-Reply-To: Message-ID: References: <20091015111107.b505b676.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: Andrew Morton , Nigel Cunningham , linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Thu, 15 Oct 2009, Hugh Dickins wrote: > On Thu, 15 Oct 2009, KAMEZAWA Hiroyuki wrote: > > On Thu, 15 Oct 2009 01:48:01 +0100 (BST) > > Hugh Dickins wrote: > > > @@ -1675,11 +1674,13 @@ static void *swap_start(struct seq_file > > > if (!l) > > > return SEQ_START_TOKEN; > > > > > > - for (i = 0; i < nr_swapfiles; i++, ptr++) { > > > - if (!(ptr->flags & SWP_USED) || !ptr->swap_map) > > > + for (type = 0; type < nr_swapfiles; type++) { > > > + smp_rmb(); /* read nr_swapfiles before swap_info[type] */ > > > + si = swap_info[type]; > > > > if (!si) ? Re-reading, I see that I missed your interjection there. Precisely because we read swap_info[type] after reading nr_swapfiles, with smp_rmb() here to enforce that, and smp_wmb() where they're set in swapon, there is no way for si to be seen as NULL here. Is there? Or are you asking for a further comment here on why that's so? I think I'd rather just switch to taking swap_lock in swap_start() and swap_next(), than be adding comments on why we don't need it. 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