From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 7 Mar 2007 02:09:11 -0800 From: Bill Irwin Subject: Re: [patch 4/6] mm: merge populate and nopage into fault (fixes nonlinear) Message-ID: <20070307100911.GO18774@holomorphy.com> References: <20070221023656.6306.246.sendpatchset@linux.site> <20070221023735.6306.83373.sendpatchset@linux.site> <20070306225101.f393632c.akpm@linux-foundation.org> <20070307070853.GB15877@wotan.suse.de> <20070307081948.GA9563@wotan.suse.de> <20070307082755.GA25733@elte.hu> <20070307003520.08b1a082.akpm@linux-foundation.org> <20070307092903.GJ18774@holomorphy.com> <20070307013942.5c0fadff.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070307013942.5c0fadff.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: Bill Irwin , Ingo Molnar , Nick Piggin , Linux Memory Management , Linux Kernel , Benjamin Herrenschmidt , Paolo 'Blaisorblade' Giarrusso List-ID: On Wed, 7 Mar 2007 01:29:03 -0800 Bill Irwin wrote: >> Guess what major real-life application not only uses nonlinear daily >> but would even be very happy to see it extended with non-vma-creating >> protections and more? On Wed, Mar 07, 2007 at 01:39:42AM -0800, Andrew Morton wrote: > uh-oh. SQL server? Close enough. ;) On Wed, 7 Mar 2007 01:29:03 -0800 Bill Irwin wrote: >> It's not terribly typical for things to be >> truncated while remap_file_pages() is doing its work, though it's been >> proposed as a method of dynamism. It won't stress remap_file_pages() vs. >> truncate() in any meaningful way, though, as userspace will be rather >> diligent about clearing in-use data out of the file offset range to be >> truncated away anyway, and all that via O_DIRECT. On Wed, Mar 07, 2007 at 01:39:42AM -0800, Andrew Morton wrote: > The problem here isn't related to truncate or direct-IO. It's just > plain-old MAP_SHARED. nonlinear VMAs are now using the old-style > dirty-memory management. msync() is basically a no-op and the code is > wildly tricky and pretty much untested. The chances that we broke it are > considerable. This would be of concern for swapping out tmpfs-backed nonlinearly- mapped files under extreme stress in Oracle's case, though it's rather typical for it all to be mlock()'d in-core and cases where that's necessary to be considered grossly underprovisioned. As far as I know, msync() is not used to manage the nonlinearly-mapped objects, which are most typically expected to be memory-backed, rendering writeback to disk of questionable value. Also quite happily, I'm not aware of any data integrity issues it would explain. Bug though it may be, it requires a usage model very rarely used by Oracle to trigger, so we've not run into it. -- wli -- 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