From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx143.postini.com [74.125.245.143]) by kanga.kvack.org (Postfix) with SMTP id C38E96B0002 for ; Wed, 27 Mar 2013 13:20:35 -0400 (EDT) Received: from /spool/local by e37.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 27 Mar 2013 11:20:34 -0600 Received: from d03relay01.boulder.ibm.com (d03relay01.boulder.ibm.com [9.17.195.226]) by d03dlp01.boulder.ibm.com (Postfix) with ESMTP id 5853E1FF004C for ; Wed, 27 Mar 2013 11:14:34 -0600 (MDT) Received: from d03av02.boulder.ibm.com (d03av02.boulder.ibm.com [9.17.195.168]) by d03relay01.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r2RHJNBe096234 for ; Wed, 27 Mar 2013 11:19:24 -0600 Received: from d03av02.boulder.ibm.com (loopback [127.0.0.1]) by d03av02.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r2RHJDxr000522 for ; Wed, 27 Mar 2013 11:19:13 -0600 Message-ID: <51532A0F.3010402@linux.vnet.ibm.com> Date: Wed, 27 Mar 2013 12:19:11 -0500 From: Seth Jennings MIME-Version: 1.0 Subject: Re: [RFC] mm: remove swapcache page early References: <1364350932-12853-1-git-send-email-minchan@kernel.org> In-Reply-To: <1364350932-12853-1-git-send-email-minchan@kernel.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Minchan Kim Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins , Dan Magenheimer , Nitin Gupta , Konrad Rzeszutek Wilk , Shaohua Li On 03/26/2013 09:22 PM, Minchan Kim wrote: > Swap subsystem does lazy swap slot free with expecting the page > would be swapped out again so we can't avoid unnecessary write. > > But the problem in in-memory swap is that it consumes memory space > until vm_swap_full(ie, used half of all of swap device) condition > meet. It could be bad if we use multiple swap device, small in-memory swap > and big storage swap or in-memory swap alone. > > This patch changes vm_swap_full logic slightly so it could free > swap slot early if the backed device is really fast. Great idea! > For it, I used SWP_SOLIDSTATE but It might be controversial. The comment for SWP_SOLIDSTATE is that "blkdev seeks are cheap". Just because seeks are cheap doesn't mean the read itself is also cheap. For example, QUEUE_FLAG_NONROT is set for mmc devices, but some of them can be pretty slow. > So let's add Ccing Shaohua and Hugh. > If it's a problem for SSD, I'd like to create new type SWP_INMEMORY > or something for z* family. Afaict, setting SWP_SOLIDSTATE depends on characteristics of the underlying block device (i.e. blk_queue_nonrot()). zram is a block device but zcache and zswap are not. Any idea by what criteria SWP_INMEMORY would be set? Also, frontswap backends (zcache and zswap) are a caching layer on top of the real swap device, which might actually be rotating media. So you have the issue of to different characteristics, in-memory caching on top of rotation media, present in a single swap device. Thanks, Seth -- 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