From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 29 Jan 2007 18:15:57 -0800 From: Andrew Morton Subject: Re: [PATCH] mm: remove global locks from mm/highmem.c Message-Id: <20070129181557.d4d17dd0.akpm@osdl.org> In-Reply-To: <45BEA41A.6020209@mbligh.org> References: <1169993494.10987.23.camel@lappy> <20070128142925.df2f4dce.akpm@osdl.org> <1170063848.6189.121.camel@twins> <45BE9FE8.4080603@mbligh.org> <20070129174118.0e922ab3.akpm@osdl.org> <45BEA41A.6020209@mbligh.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: "Martin J. Bligh" Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Ingo Molnar , David Chinner List-ID: On Mon, 29 Jan 2007 17:49:14 -0800 "Martin J. Bligh" wrote: > Andrew Morton wrote: > > On Mon, 29 Jan 2007 17:31:20 -0800 > > "Martin J. Bligh" wrote: > > > >> Peter Zijlstra wrote: > >>> On Sun, 2007-01-28 at 14:29 -0800, Andrew Morton wrote: > >>> > >>>> As Christoph says, it's very much preferred that code be migrated over to > >>>> kmap_atomic(). Partly because kmap() is deadlockable in situations where a > >>>> large number of threads are trying to take two kmaps at the same time and > >>>> we run out. This happened in the past, but incidences have gone away, > >>>> probably because of kmap->kmap_atomic conversions. > >>>> From which callsite have you measured problems? > >>> CONFIG_HIGHPTE code in -rt was horrid. I'll do some measurements on > >>> mainline. > >>> > >> CONFIG_HIGHPTE is always horrid -we've known that for years. > > > > We have? What's wrong with it? > > http://www.ussg.iu.edu/hypermail/linux/kernel/0307.0/0463.html 2% overhead for a pte-intensive workload for unknown reasons four years ago. Sort of a mini-horrid, no? We still don't know what is the source of kmap() activity which necessitated this patch btw. AFAIK the busiest source is ext2 directories, but perhaps NFS under certain conditions? ->prepare_write no longer requires that the caller kmap the page. -- 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