From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id 77FFD6B00AC for ; Fri, 18 Sep 2009 03:55:24 -0400 (EDT) Subject: Re: [PATCH 2/4] send callback when swap slot is freed From: Pekka Enberg In-Reply-To: References: <1253227412-24342-1-git-send-email-ngupta@vflare.org> <1253227412-24342-3-git-send-email-ngupta@vflare.org> <1253256805.4959.8.camel@penberg-laptop> Date: Fri, 18 Sep 2009 10:55:28 +0300 Message-Id: <1253260528.4959.13.camel@penberg-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Hugh Dickins Cc: Nitin Gupta , Greg KH , Andrew Morton , Ed Tomlinson , linux-kernel , linux-mm , linux-mm-cc , kamezawa.hiroyu@jp.fujitsu.com, nishimura@mxp.nes.nec.co.jp List-ID: Hi Hugh, On Fri, 2009-09-18 at 08:17 +0100, Hugh Dickins wrote: > On Fri, 18 Sep 2009, Pekka Enberg wrote: > > On Fri, 2009-09-18 at 04:13 +0530, Nitin Gupta wrote: > > > +EXPORT_SYMBOL_GPL(set_swap_free_notify); > > > + > > > static int swap_entry_free(struct swap_info_struct *p, > > > swp_entry_t ent, int cache) > > > { > > > @@ -585,6 +617,8 @@ static int swap_entry_free(struct swap_info_struct *p, > > > swap_list.next = p - swap_info; > > > nr_swap_pages++; > > > p->inuse_pages--; > > > + if (p->swap_free_notify_fn) > > > + p->swap_free_notify_fn(p->bdev, offset); > > > } > > > if (!swap_count(count)) > > > mem_cgroup_uncharge_swap(ent); > > > > OK, this hits core kernel code so we need to CC some more mm/swapfile.c > > people. The set_swap_free_notify() API looks strange to me. Hugh, I > > think you mentioned that you're okay with an explicit hook. Any > > suggestions how to do this cleanly? > > No, no better suggestion. I quite see Nitin's point that ramzswap > would benefit significantly from a callback here, though it's not a > place (holding swap_lock) where we'd like to offer a callback at all. > > I think I would prefer the naming to make it absolutely clear that > it's a special for ramzswap or compcache, rather than dressing it > up in the grand generality of a swap_free_notify_fn: giving our > hacks fancy names doesn't really make them better. > > (Does the bdev matching work out if there are any regular swapfiles > around? I've not checked, might or might not need refinement there.) The *hook* looks OK to me but set_swap_free_notify() looks like an ugly hack. I don't understand why we're setting up the hook lazily in ramzswap_read() nor do I understand why we need to look up struct swap_info_struct with a bdev. Surely there's a cleaner way to do all this? Probably somewhere in sys_swapon()? Pekka -- 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