From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id 1DD356B0069 for ; Wed, 2 Nov 2011 15:46:26 -0400 (EDT) Message-ID: <4EB19DE5.4080108@redhat.com> Date: Wed, 02 Nov 2011 15:45:41 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [GIT PULL] mm: frontswap (for 3.2 window) 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> <1320005162.15403.14.camel@nimitz> In-Reply-To: <1320005162.15403.14.camel@nimitz> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: Dan Magenheimer , 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 10/30/2011 04:06 PM, Dave Hansen wrote: > 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. My only real behaviour concern with tmem is that /proc/sys/overcommit_memory will no longer be able to do anything useful, since we'll never know in advance how much memory is available. That may be outweighed by the benefits of having more memory available than before, and a reasonable tradeoff to make for the users. That leaves us with having the code cleaned up to reasonable standards. To be honest, I would rather have larger hooks in the existing mm code, than exported variables and having the hooks live elsewhere (where people changing the "normal" mm code won't see it, and are more likely to break it). -- 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