Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752660Ab1F1XES (ORCPT ); Tue, 28 Jun 2011 19:04:18 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:38288 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751205Ab1F1XEL (ORCPT ); Tue, 28 Jun 2011 19:04:11 -0400 Date: Tue, 28 Jun 2011 16:03:47 -0700 From: Andrew Morton To: Andrea Righi Cc: Minchan Kim , Peter Zijlstra , Johannes Weiner , KAMEZAWA Hiroyuki , Andrea Arcangeli , Hugh Dickins , Jerry James , Marcus Sorensen , Matt Heaton , KOSAKI Motohiro , Rik van Riel , Theodore Tso , Shaohua Li , =?ISO-8859-1?Q?P?= =?ISO-8859-1?Q?=E1draig?= Brady , linux-mm , LKML Subject: Re: [PATCH v4 0/2] fadvise: move active pages to inactive list with POSIX_FADV_DONTNEED Message-Id: <20110628160347.a5ffcc26.akpm@linux-foundation.org> In-Reply-To: <20110628225645.GB2274@thinkpad> References: <1309181361-14633-1-git-send-email-andrea@betterlinux.com> <20110628151233.f0a279be.akpm@linux-foundation.org> <20110628225645.GB2274@thinkpad> X-Mailer: Sylpheed 3.0.2 (GTK+ 2.20.1; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2210 Lines: 54 On Wed, 29 Jun 2011 00:56:45 +0200 Andrea Righi wrote: > > > > > > In this way if the backup was the only user of a page, that page will be > > > immediately removed from the page cache by calling POSIX_FADV_DONTNEED. If the > > > page was also touched by other processes it'll be moved to the inactive list, > > > having another chance of being re-added to the working set, or simply reclaimed > > > when memory is needed. > > > > So if an application touches a page twice and then runs > > POSIX_FADV_DONTNEED, that page will now not be freed. > > > > That's a big behaviour change. For many existing users > > POSIX_FADV_DONTNEED simply doesn't work any more! > > Yes. This is the main concern that was raised by P__draig. > > > > > I'd have thought that adding a new POSIX_FADV_ANDREA would be safer > > than this. > > Actually Jerry (in cc) proposed > POSIX_FADV_IDONTNEEDTHISBUTIFSOMEBODYELSEDOESTHENDONTTOUCHIT in a > private email. :) Sounds good. Needs more underscores though. > > > > > > The various POSIX_FADV_foo's are so ill-defined that it was a mistake > > to ever use them. We should have done something overtly linux-specific > > and given userspace more explicit and direct pagecache control. > > That would give us the possibility to implement a wide range of > different operations (drop, drop if used once, add to the active list, > add to the inactive list, etc..). Some users always complain that they > would like to have a better control over the page cache from userspace. Well, I'd listen to proposals ;) One thing we must be careful about is to not expose things like "active list" to userspace. linux-4.5 may not _have_ an active list, and its implementors would hate us and would have to jump through hoops to implement vaguely compatible behaviour in the new scheme. So any primitives which are exposed should be easily implementable and should *make sense* within any future scheme... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/