From mboxrd@z Thu Jan 1 00:00:00 1970 From: Blaisorblade Subject: Re: [patch 4/6] mm: merge populate and nopage into fault (fixes nonlinear) Date: Tue, 13 Mar 2007 00:01:13 +0100 References: <20070221023735.6306.83373.sendpatchset@linux.site> <20070307094947.GE8609@wotan.suse.de> <20070307100242.GG8609@wotan.suse.de> In-Reply-To: <20070307100242.GG8609@wotan.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200703130001.13467.blaisorblade@yahoo.it> Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: Bill Irwin , Ingo Molnar , Andrew Morton , Linux Memory Management , Linux Kernel , Benjamin Herrenschmidt List-ID: On Wednesday 07 March 2007 11:02, Nick Piggin wrote: > On Wed, Mar 07, 2007 at 10:49:47AM +0100, Nick Piggin wrote: > > On Wed, Mar 07, 2007 at 01:44:20AM -0800, Bill Irwin wrote: > > > On Wed, Mar 07, 2007 at 10:28:21AM +0100, Nick Piggin wrote: > > > > Depending on whether anyone wants it, and what features they want, we > > > > could emulate the old syscall, and make a new restricted one which is > > > > much less intrusive. > > > > For example, if we can operate only on MAP_ANONYMOUS memory and > > > > specify that nonlinear mappings effectively mlock the pages, then we > > > > can get rid of all the objrmap and unmap_mapping_range handling, > > > > forget about the writeout and msync problems... > > > > > > Anonymous-only would make it a doorstop for Oracle, since its entire > > > motive for using it is to window into objects larger than user virtual > > > > Uh, duh yes I don't mean MAP_ANONYMOUS, I was just thinking of the shmem > > inode that sits behind MAP_ANONYMOUS|MAP_SHARED. Of course if you don't > > have a file descriptor to get a pgoff, then remap_file_pages is a > > doorstop for everyone ;) > > > > > address spaces (this likely also applies to UML, though they should > > > really chime in to confirm). Restrictions to tmpfs and/or ramfs would > > > likely be liveable, though I suspect some things might want to do it to > > > shm segments (I'll ask about that one). There's definitely no need for > > > a persistent backing store for the object to be remapped in Oracle's > > > case, in any event. It's largely the in-core destination and source of > > > IO, not something saved on-disk itself. > > > > Yeah, tmpfs/shm segs are what I was thinking about. If UML can live with > > that as well, then I think it might be a good option. > > Oh, hmm.... if you can truncate these things then you still need to > force unmap so you still need i_mmap_nonlinear. Well, we don't need truncate(), but MADV_REMOVE for memory hotunplug, which is way similar I guess. About the restriction to tmpfs, I have just discovered '[PATCH] mm: tracking shared dirty pages' (commit d08b3851da41d0ee60851f2c75b118e1f7a5fc89), which already partially conflicts with remap_file_pages for file-based mmaps (and that's fully fine, for now). Even if UML does not need it, till now if there is a VMA protection and a page hasn't been remapped with remap_file_pages, the VMA protection is used (just because it makes sense). However, it is only used when the PTE is first created - we can never change protections on a VMA - so it vma_wants_writenotify() is true (on all file-based and on no shmfs based mapping, right?), and we write-protect the VMA, it will always be write-protected. That's no problem for UML, but for any other user (I guess I'll have to prevent callers from trying such stuff - I started from a pretty generic patch). > But come to think of it, I still don't think nonlinear mappings are > too bad as they are ;) Btw, I really like removing ->populate and merging the common code together. filemap_populate and shmem_populate are so obnoxiously different that I already wanted to do that (after merging remap_file_pages() core). Also, I'm curious. Since my patches are already changing remap_file_pages() code, should they be absolutely merged after yours? -- Inform me of my mistakes, so I can add them to my list! Paolo Giarrusso, aka Blaisorblade http://www.user-mode-linux.org/~blaisorblade Chiacchiera con i tuoi amici in tempo reale! http://it.yahoo.com/mail_it/foot/*http://it.messenger.yahoo.com -- 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