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 ESMTP id D6AC46B0069 for ; Sun, 30 Oct 2011 16:06:35 -0400 (EDT) Received: from /spool/local by e36.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sun, 30 Oct 2011 14:06:35 -0600 Received: from d03av01.boulder.ibm.com (d03av01.boulder.ibm.com [9.17.195.167]) by d03relay02.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p9UK6CAd128010 for ; Sun, 30 Oct 2011 14:06:12 -0600 Received: from d03av01.boulder.ibm.com (loopback [127.0.0.1]) by d03av01.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p9UK6BdU009421 for ; Sun, 30 Oct 2011 14:06:12 -0600 Subject: RE: [GIT PULL] mm: frontswap (for 3.2 window) From: Dave Hansen In-Reply-To: <3ac142d4-a4ca-4a24-bf0b-69a90bd1d1a0@default> References: <75efb251-7a5e-4aca-91e2-f85627090363@default> <20111027215243.GA31644@infradead.org> <1319785956.3235.7.camel@lappy> <552d2067-474d-4aef-a9a4-89e5fd8ef84f@default> <20111028163053.GC1319@redhat.com> <20138.62532.493295.522948@quad.stoffel.home> <3982e04f-8607-4f0a-b855-2e7f31aaa6f7@default 20139.5644.583790.903531@quad.stoffel.home> <3ac142d4-a4ca-4a24-bf0b-69a90bd1d1a0@default> Content-Type: text/plain; charset="UTF-8" Date: Sun, 30 Oct 2011 13:06:02 -0700 Message-ID: <1320005162.15403.14.camel@nimitz> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Dan Magenheimer Cc: John Stoffel , Johannes Weiner , Pekka Enberg , Cyclonus J , Sasha Levin , Christoph Hellwig , David Rientjes , Linus Torvalds , linux-mm@kvack.org, LKML , Andrew Morton , Konrad Wilk , Jeremy Fitzhardinge , Seth Jennings , ngupta@vflare.org, Chris Mason , JBeulich@novell.com, Jonathan Corbet On Sun, 2011-10-30 at 12:18 -0700, Dan Magenheimer wrote: > > since they're the ones who will have to understand this stuff and know > > how to maintain it. And keeping this maintainable is a key goal. > > Absolutely agree. Count the number of frontswap lines that affect > the current VM core code and note also how they are very clearly > identified. It really is a very VERY small impact to the core VM > code (e.g. in the files swapfile.c and page_io.c). Granted, the impact on the core VM in lines of code is small. But, I think the behavioral impact is potentially huge since tmem's hooks add non-trivial amounts of framework underneath the VM in core paths. In zcache's case, this means a bunch of allocations and an entirely new allocator memory allocator being used in the swap paths. We're certainly still shaking bugs out of the interactions there like with zcache_direct_reclaim_lock. Granted, that's not a tmem/frontswap/cleancache bug, but it does speak to the difficulty and subtlety of writing one of those frameworks underneath the tmem API. -- Dave -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org