From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755620Ab0JSWcI (ORCPT ); Tue, 19 Oct 2010 18:32:08 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:35069 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754651Ab0JSWcG (ORCPT ); Tue, 19 Oct 2010 18:32:06 -0400 Date: Tue, 19 Oct 2010 15:31:36 -0700 From: Andrew Morton To: Kay Sievers Cc: linux-kernel , Greg KH Subject: Re: [PATCH] support polling of /proc/swaps Message-Id: <20101019153136.b2543f7b.akpm@linux-foundation.org> In-Reply-To: <1287479956.1729.1.camel@yio.site> References: <1287479956.1729.1.camel@yio.site> X-Mailer: Sylpheed 2.4.8 (GTK+ 2.12.9; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 19 Oct 2010 11:19:16 +0200 Kay Sievers wrote: > From: Kay Sievers > Subject: support polling of /proc/swaps > > System management wants to subscribe to changes in swap > configuration. Make /proc/swaps pollable like /proc/mounts. > It's a bit sad that we have to add quite a pile of infrastructure to make a procfs file pollable. I wonder if it's possible to provide some core support for this, and reduce the amount of code at each particular handler site. Also, I wonder how we are to communicate the existence of this feature to our users. Nobody will look in Documentation/filesystems/. Is there a manpage? Seems not... > --- > mm/swapfile.c | 48 +++++++++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 47 insertions(+), 1 deletion(-) > > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -30,6 +30,7 @@ > #include > #include > #include > +#include > > #include > #include > @@ -58,6 +59,9 @@ static struct swap_info_struct *swap_inf > > static DEFINE_MUTEX(swapon_mutex); > > +static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait); > +static int proc_poll_event; Please pick a lock to protect proc_poll_event. Then document that locking here, when you also document proc_poll_event ;) > static inline unsigned char swap_count(unsigned char ent) > { > return ent & ~SWAP_HAS_CACHE; /* may include SWAP_HAS_CONT flag */ > @@ -1680,6 +1684,8 @@ SYSCALL_DEFINE1(swapoff, const char __us > } > filp_close(swap_file, NULL); > err = 0; > + proc_poll_event++; Then fix this race. > + wake_up_interruptible(&proc_poll_wait); > > out_dput: > filp_close(victim, NULL);