From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id 7765F9000BD for ; Mon, 27 Jun 2011 07:54:26 -0400 (EDT) Message-ID: <4E086F51.50403@draigBrady.com> Date: Mon, 27 Jun 2011 12:53:53 +0100 From: =?ISO-8859-1?Q?P=E1draig_Brady?= MIME-Version: 1.0 Subject: Re: [PATCH v3 0/2] fadvise: support POSIX_FADV_NOREUSE References: <1308923350-7932-1-git-send-email-andrea@betterlinux.com> <4E07F349.2040900@jp.fujitsu.com> <20110627071139.GC1247@thinkpad> <4E0858CF.6070808@draigBrady.com> <20110627102933.GA1282@thinkpad> In-Reply-To: <20110627102933.GA1282@thinkpad> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrea Righi Cc: KOSAKI Motohiro , akpm@linux-foundation.org, minchan.kim@gmail.com, riel@redhat.com, peterz@infradead.org, hannes@cmpxchg.org, kamezawa.hiroyu@jp.fujitsu.com, aarcange@redhat.com, hughd@google.com, jamesjer@betterlinux.com, marcus@bluehost.com, matt@bluehost.com, tytso@mit.edu, shaohua.li@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org On 27/06/11 11:29, Andrea Righi wrote: > The actual problem I think is that apps expect that DONTNEED can be used > to drop cache, but this is not written anywhere in the POSIX standard. > > I would also like to have both functionalities: 1) be sure to drop page > cache pages (now there's only a system-wide knob to do this: > /proc/sys/vm/drop_caches), 2) give an advice to the kernel that I will > not reuse some pages in the future. > > The standard can only provide 2). If we also want 1) at the file > granularity, I think we'd need to introduce something linux specific to > avoid having portability problems. True, though Linux is the reference for posix_fadvise() implementations, given its lack of support on other platforms. So just to summarize for _my_ reference. You're changing DONTNEED to mean "drop if !PageActive()". I.E. according to http://linux-mm.org/PageReplacementDesign "drop if files only accessed once". This will mean that there is no way currently to remove a particular file from the cache on linux. Hopefully that won't affect any of: http://codesearch.google.com/#search/&q=POSIX_FADV_DONTNEED Ideally I'd like cache functions for: DROP, ADD, ADD if space1 which could correspond to: DONTNEED, WILLNEED, NOREUSE but what we're going for are these somewhat overlapping functions: DROP if used once2, ADD, ADD if space cheers, Padraig. 1 Not implemented yet. 2 Hopefully there are no access patterns a single process can do to make a PageActive as that would probably not be desired in relation to "Drop if used once" functionality. -- 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