From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id 43D196B004D for ; Wed, 23 Sep 2009 23:11:56 -0400 (EDT) Received: by gxk19 with SMTP id 19so423070gxk.10 for ; Wed, 23 Sep 2009 20:11:59 -0700 (PDT) Message-ID: <4ABAE340.7010403@vflare.org> Date: Thu, 24 Sep 2009 08:40:56 +0530 From: Nitin Gupta Reply-To: ngupta@vflare.org MIME-Version: 1.0 Subject: Re: [PATCH RFC 1/2] Add notifiers for various swap events References: <1253540040-24860-1-git-send-email-ngupta@vflare.org> <20090924104708.4f54ce4e.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20090924104708.4f54ce4e.kamezawa.hiroyu@jp.fujitsu.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: Hugh Dickins , Pekka Enberg , linux-kernel , linux-mm List-ID: On 09/24/2009 07:17 AM, KAMEZAWA Hiroyuki wrote: > On Mon, 21 Sep 2009 19:03:59 +0530 > Nitin Gupta wrote: > >> Add notifiers for following swap events: >> - Swapon >> - Swapoff >> - When a swap slot is freed >> >> This is required for ramzswap module which implements RAM based block >> devices to be used as swap disks. These devices require a notification >> on these events to function properly (as shown in patch 2/2). >> >> Currently, I'm not sure if any of these event notifiers have any other >> users. However, adding ramzswap specific hooks instead of this generic >> approach resulted in a bad/hacky code. >> > Hmm ? if it's not necessary to make ramzswap as module, for-ramzswap-only > code is much easier to read.. > The patches posted earlier (v3 patches) inserts special hooks for swap slot free event only. In this version, the callback is set when we get first R/W request. Actually ramzswap needs callback for swapon/swapoff too but I just didn't do it. Then Pekka posted test patch that allows setting this callback during swapon itself. Looking that all these patches, I realized its already too messy even if we just make everything ramzswap specific. Just FYI, Pekka's test patch: http://patchwork.kernel.org/patch/48472/ Then I added this generic notifier interface which, compared to earlier version, looks much cleaner. The code to add these notifiers is also very small. > > >> For SWAP_EVENT_SLOT_FREE, callbacks are made under swap_lock. Currently, this >> is not a problem since ramzswap is the only user and the callback it registers >> can be safely made under this lock. However, if this event finds more users, >> we might have to work on reducing contention on this lock. >> >> Signed-off-by: Nitin Gupta >> > > In general, notifier chain codes allowed to return NOTIFY_BAD. > But this patch just assumes all chains should return NOTIFY_OK or > just ignore return code. > > That's not good as generic interface, I think. What action we can take here if the notifier_call_chain() returns an error (apart from maybe printing an error)? Perhaps we can add a warning in case of swapon/off events but not in case of swap slot free event which is called under swap_lock. Thanks, Nitin -- 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