On Fri, 9 Feb 2007 11:32:58 +0100 Nick Piggin <npiggin@xxxxxxx> wrote: > On Fri, Feb 09, 2007 at 02:09:54AM -0800, Andrew Morton wrote: > > On Fri, 9 Feb 2007 10:54:05 +0100 Nick Piggin <npiggin@xxxxxxx> wrote: > > > > > > > > That's still got a deadlock, > > > > It does? > > Yes, PG_lock vs mm->mmap_sem. Where? It requires that someone hold mmap_sem for writing as well as a page lock (in an order which would require some thought). Do we ever do that? > > > and also it doesn't work if we want to lock > > > the page when performing a minor fault (which I want to fix fault vs > > > invalidate), > > > > It's hard to discuss this without a description of what you want to fix > > there, and a description of how you plan to fix it. > > http://marc.theaimsgroup.com/?l=linux-mm&m=116865911432667&w=2 mutter. Could perhaps fix that by running ClearPageUptodate in invalidate, thus forcing the pagefault code to take the page lock (which we already hold). That does mean that we'll fleetingly have a non-uptodate page in pagetables which is a bit nasty. Or, probably better, we could add a new page flag (heh) telling nopage that it needs to lock the page even if it's uptodate. > > > and also assumes nobody's ->nopage locks the page or > > > requires any resources that are held by prepare_write (something not > > > immediately clear to me with the cluster filesystems, at least). > > > > The nopage handler is filemap_nopage(). Are there any exceptions to that? > > OCFS2 and GFS2. So the rule is that ->nopage handlers against pagecache mustn't lock the page if it's already uptodate. That's OK. But it might conflict with the above invalidate proposal. Gad. ocfs2_nopage() diddles with signals. > > > But that all becomes legacy path, so do we really care? Supposing fs > > > maintainers like perform_write, then after the main ones have implementations > > > we could switch over to the slow-but-correct prepare_write legacy path. > > > Or we could leave it, or we could use Linus's slightly-less-buggy scheme... > > > by that point I expect I'd be sick of arguing about it ;) > > > > It's worth "arguing" about. This is write(). What matters more?? > > That's the legacy path that uses prepare/commit (ie. supposing that all > major filesystems did get converted to perform_write). We'll never, ever, ever update and test all filesytems. What you're calling "legacy" code will be there for all time. I haven't had time to look at the perform_write stuff yet. > Of course I would still want my correct-but-slow version in that case, > but I just wouldn't care to argue if you still wanted to keep it fast. This is write(). We just cannot go and double-copy all the memory or take mmap_sem and do a full pagetable walk in there. It just means that we haven't found a suitable solution yet. - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
