On Sun, 2007-09-02 at 16:17 +0200, Nick Piggin wrote: > On Sun, Sep 02, 2007 at 02:48:04PM +0100, David Woodhouse wrote: > > On Sun, 2007-09-02 at 15:20 +0200, Nick Piggin wrote: > > > OK, but then hasn't the patch just made the deadlock harder to hit, > > > or is there some invariant that says that readpage() will never be > > > invoked if gc was invoked on the same page as we're commit_write()ing? > > > > > The Q/A comments aren't very sure about this. I guess from the look > > > of it, prepare_write/commit_write make sure the page will be uptodate > > > by the start of commit_write, > > > > That's the intention, yes. > > > > > and you avoid GCing the page in > > > prepare_write because your new page won't have any nodes allocated > > > yet that can possibly be GCed? > > > > We _might_ GC the page -- it might not be a new page; we might be > > overwriting it. But it's fine if we do. Actually it's slightly > > suboptimal because we'll write out the same data twice -- once in GC and > > then immediately afterward in the write which we were making space for. > > But doesn't GC only happen in prepare_write in the case that the > i_size is being extended into a new page?
Ah, yes. I was thinking of commit_write, and it had temporarily escaped my notice that we also write in prepare_write, to extend the file. So yes, you're probably right that it doesn't matter; in any GC triggered from _prepare_write_ we avoid GCing the page in question because it by definition doesn't exist. -- dwmw2 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
