On Thu, Jun 2, 2011 at 2:54 AM, Jan Kara <jack@xxxxxxx> wrote: > On Tue 31-05-11 18:27:20, Ted Tso wrote: >> On Tue, May 31, 2011 at 01:22:53PM +0200, Jan Kara wrote: >> > >> > The problem is that with ext4, we need i_mutex in io completion path to >> > end page writeback. So we cannot do GFP_KERNEL allocation whenever we hold >> > i_mutex because mm might wait in direct reclaim for IO to complete and that >> > cannot happen until we release i_mutex. >> >> OK, maybe I'm being dense, but I'm not seeing it. I see where we need >> i_mutex on the ext4_da_writepages() codepath, but that's never used >> for direct reclaim. Direct reclaim only calls ext4_writepage(), and >> that doesn't seem to try to grab i_mutex as near as I can tell. Am I >> missing something? > What happens is that direct reclaim sometimes does > wait_on_page_writeback() (e.g. shrink_page_list()) or it explicitely waits > for NR_WRITEBACK statistics to go below some threshold > (throttle_vm_writeout()). And that is deadlockable if we hold i_mutex while > doing this because we may need i_mutex to actually move the page from > PageWriteback state... > > As I'm saying this, I've realized ext4 has this problem also with > stable-pages patches because there we can wait for PageWriteback in > grab_cache_page_write_begin() when we also hold i_mutex. So I think we'll > have to come up with a way to convert unwritten extents without having to > hold i_mutex. That's going to be interesting. Hi Jan/Ted, Does that mean I should remove the whole JBD2_TOPLEVEL thing from my revised patch ? Or should I fix it as per your feedback in the other patch ? -- Thanks - Manish -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
