On Wed, 21 May 2008 18:52:27 +0100 (BST) Hugh Dickins <hugh@xxxxxxxxxxx> wrote: > On Tue, 20 May 2008, Andrew Morton wrote: > > On Wed, 21 May 2008 10:15:32 +0400 Evgeniy Polyakov <johnpol@xxxxxxxxxxx> wrote: > > > On Tue, May 20, 2008 at 04:28:16PM -0700, Andrew Morton (akpm@xxxxxxxxxxxxxxxxxxxx) wrote: > > > > It's more than efficiency. There are lots and lots of things we cannot > > > > do in direct-reclaim context. > > > > > > > > ... > > > > > > > > c) Cannot run iput(). Or at least, we couldn't five or six years > > > > ago. afaik nobody has investigated whether the situation is now > > > > better or worse. > > I happened to notice your remark in the buffer heads defrag thread. > Do you remember what that limitation was about? Ages and ages ago. I expect it was a deadlock thing. iput_final() can end up calling things like write_inode() which can want to do things like opening a transaction against filesystem A while already having one open against filesystem B. Which is both deadlockable and BUGable. It will take other embarrassing locks too, probably. > Because just a few months ago I discovered a shmem race which I fixed > by doing igrab+iput in shmem_writepage, in the reclaim context. Feeling > guilty now: I'd better investigate, but would welcome a starting pointer. > > (If I'm lucky, it'll be that the generic code in vmscan.c cannot > use iput, but particular filesystems might themselves be safe to.) Yes, it was specific to the direct-reclaim calling context. -- 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
