From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 31 Jan 2007 14:22:24 +1100 From: David Chinner Subject: Re: [PATCH] mm: remove global locks from mm/highmem.c Message-ID: <20070131032224.GV44411608@melbourne.sgi.com> 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> <20070129181557.d4d17dd0.akpm@osdl.org> <20070131004436.GS44411608@melbourne.sgi.com> <20070130171132.7be3b054.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070130171132.7be3b054.akpm@osdl.org> Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: David Chinner , "Martin J. Bligh" , Peter Zijlstra , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Ingo Molnar List-ID: On Tue, Jan 30, 2007 at 05:11:32PM -0800, Andrew Morton wrote: > On Wed, 31 Jan 2007 11:44:36 +1100 > David Chinner wrote: > > > On Mon, Jan 29, 2007 at 06:15:57PM -0800, Andrew Morton wrote: > > > 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. > > > > Agreed, but don't we (xfs_iozero) have to map it first to zero it? > > > > I think what you are saying here, Andrew, is that we can > > do something like: > > > > page = grab_cache_page > > ->prepare_write(page) > > kaddr = kmap_atomic(page, KM_USER0) > > memset(kaddr+offset, 0, bytes) > > flush_dcache_page(page) > > kunmap_atomic(kaddr, KM_USER0) > > ->commit_write(page) > > > > to avoid using kmap() altogether? > > Yup. Even better, use clear_highpage(). For even more goodness, clearmem_highpage_flush() does exactly the right thing for partial page zeroing ;) Thanks, Andrew, I've added a patch to my QA tree with this mod. Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group -- 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