On Sat 06-11-10 02:36:14, Johannes Weiner wrote: > Can you please keep linux-mm@xxxxxxxxx in the loop on writeback stuff? Will do. Sorry for that. Honza > I Cc'd it now, here is the full quote: > > On Fri, Nov 05, 2010 at 10:26:23PM +0100, Jan Kara wrote: > > When wb_writeback() is called in WB_SYNC_ALL mode, work->nr_to_write is usually > > set to LONG_MAX. The logic in wb_writeback() then calls __writeback_inodes_sb() > > with nr_to_write == MAX_WRITEBACK_PAGES and thus we easily end up with negative > > nr_to_write after the function returns. wb_writeback() then decides we need > > another round of writeback but this is wrong in some cases! For example when > > a single large file is continuously dirtied, we would never finish syncing > > it because each pass would be able to write MAX_WRITEBACK_PAGES and inode dirty > > timestamp never gets updated (as inode is never completely clean). > > > > Fix the issue by setting nr_to_write to LONG_MAX in WB_SYNC_ALL mode. We do not > > need nr_to_write in WB_SYNC_ALL mode anyway since livelock avoidance is done > > differently for it. > > > > After this patch, program from http://lkml.org/lkml/2010/10/24/154 is no longer > > able to stall sync forever. > > > > Signed-off-by: Jan Kara <jack@xxxxxxx> > > --- > > fs/fs-writeback.c | 18 ++++++++++++++---- > > 1 files changed, 14 insertions(+), 4 deletions(-) > > > > Fengguang, I've been testing with those writeback fixes you reposted > > a few days ago and I've been able to still reproduce livelocks with > > Jan Engelhard's test case. Using writeback tracing I've tracked the > > problem to the above and with this patch, sync finishes OK (well, it still > > takes about 15 minutes but that's about expected time given the throughput > > I see to the disk - the test case randomly dirties pages in a huge file). > > So could you please add this patch to the previous two send them to Jens > > for inclusion? > > > > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c > > index 6b4d02a..d5873a6 100644 > > --- a/fs/fs-writeback.c > > +++ b/fs/fs-writeback.c > > @@ -629,6 +629,7 @@ static long wb_writeback(struct bdi_writeback *wb, > > }; > > unsigned long oldest_jif; > > long wrote = 0; > > + long write_chunk; > > struct inode *inode; > > > > if (wbc.for_kupdate) { > > @@ -640,6 +641,15 @@ static long wb_writeback(struct bdi_writeback *wb, > > wbc.range_start = 0; > > wbc.range_end = LLONG_MAX; > > } > > + /* > > + * In WB_SYNC_ALL mode, we just want to ignore nr_to_write as > > + * we need to write everything and livelock avoidance is implemented > > + * differently. > > + */ > > + if (wbc.sync_mode == WB_SYNC_NONE) > > + write_chunk = MAX_WRITEBACK_PAGES; > > + else > > + write_chunk = LONG_MAX; > > > > wbc.wb_start = jiffies; /* livelock avoidance */ > > for (;;) { > > @@ -665,7 +675,7 @@ static long wb_writeback(struct bdi_writeback *wb, > > break; > > > > wbc.more_io = 0; > > - wbc.nr_to_write = MAX_WRITEBACK_PAGES; > > + wbc.nr_to_write = write_chunk; > > wbc.pages_skipped = 0; > > > > trace_wbc_writeback_start(&wbc, wb->bdi); > > @@ -675,8 +685,8 @@ static long wb_writeback(struct bdi_writeback *wb, > > writeback_inodes_wb(wb, &wbc); > > trace_wbc_writeback_written(&wbc, wb->bdi); > > > > - work->nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; > > - wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write; > > + work->nr_pages -= write_chunk - wbc.nr_to_write; > > + wrote += write_chunk - wbc.nr_to_write; > > > > /* > > * If we consumed everything, see if we have more > > @@ -691,7 +701,7 @@ static long wb_writeback(struct bdi_writeback *wb, > > /* > > * Did we write something? Try for more > > */ > > - if (wbc.nr_to_write < MAX_WRITEBACK_PAGES) > > + if (wbc.nr_to_write < write_chunk) > > continue; > > /* > > * Nothing written. Wait for some inode to > > -- > > 1.7.1 > > > > -- > > 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 -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- 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
