On Tue, Sep 15, 2009 at 04:01:45PM +0200, Jan Kara wrote: > On Tue 15-09-09 09:08:29, Christoph Hellwig wrote: > > On Tue, Sep 15, 2009 at 03:04:19PM +0200, Jens Axboe wrote: > > > > > > > Let's have a look at the flags in wbc: > > > > nonblocking - Currently only set by direct callers of ->writepage() BUT > > > > originally wb_kupdate() and background_writeout() also > > > > set this flag. Since filesystems and write_cache_pages() > > > > use the flag we should set it for equivalent writeouts as > > > > well. This should be fixed... > > > > > > Since this is all handled by the dedicated thread now, dropping the > > > nonblocking bit was on purpose. What would the point be, except for > > > stopping pdflush being blocked on request allocation? > > > > Note that this flag just caused utter mess traditionally. btrfs decided > > to ignore it completely and ext4 partially. Removing this check in > > XFS increases large bufferd write loads massively. > > > > Just half-removing it is a bad idea, though - if you don't set it > > anymore please kill it entirely. > The nonblocking flag is still set for writeback done for memory reclaim. > OTOH the only real consumer of this flag now seems to be > __block_write_full_page() which does trylock_buffer() in case of > nonblocking writeback. I'm undecided whether it makes sence or not. Ugh, making sense is tricky to say. If __block_write_full_page does a lock_buffer() instead of a trylock_buffer(), and ext3 is mounted in data=ordered mode then it is very possible that we'll end up with a dirty page with locked buffers. The buffers will have been locked by ext3 data=ordered writeback and they won't unlock until the IO is done. We probably don't want kswapd waiting on that writeback. -chris -- 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
