On Tue, 2007-10-02 at 10:00 +0800, Fengguang Wu wrote: > On Mon, Oct 01, 2007 at 11:57:34AM -0400, Chuck Ebbert wrote: > > On 09/29/2007 07:04 AM, Fengguang Wu wrote: ... > > (expecting real world confirmations...) > > Here is a new safer version. It's more ugly though. > > --- > writeback: avoid possible balance_dirty_pages() lockup on a light-load bdi > > On a busy-writing system, a writer could be hold up infinitely on a > light-load device. It will be trying to sync more than available dirty data. > > The problem case: > > 0. sda/nr_dirty >= dirty_limit; > sdb/nr_dirty == 0 > 1. dd writes 32 pages on sdb > 2. balance_dirty_pages() blocks dd, and tries to write 6MB. > 3. it never gets there: there's only 128KB dirty data. > 4. dd may be blocked for a loooong time > > Fix it by returning on 'zero dirty inodes' in the current bdi. > (In fact there are slight differences between 'dirty inodes' and 'dirty > pages'. > But there is no available counters for 'dirty pages'.) > > But the newly introduced 'break' could make the nr_writeback drift away > above the dirty limit. The workaround is to limit the error under 1MB. > > Cc: Chuck Ebbert <[EMAIL PROTECTED]> > Cc: Peter Zijlstra <[EMAIL PROTECTED]> > Signed-off-by: Fengguang Wu <[EMAIL PROTECTED]> > --- > mm/page-writeback.c | 5 +++++ > 1 file changed, 5 insertions(+) > > --- linux-2.6.22.orig/mm/page-writeback.c > +++ linux-2.6.22/mm/page-writeback.c > @@ -250,6 +250,11 @@ static void balance_dirty_pages(struct a > pages_written += write_chunk - wbc.nr_to_write; > if (pages_written >= write_chunk) > break; /* We've done our duty */ > + if (list_empty(&mapping->host->i_sb->s_dirty) && > + list_empty(&mapping->host->i_sb->s_io) && > + nr_reclaimable + global_page_state(NR_WRITEBACK) <= > + dirty_thresh + (1 << (20-PAGE_CACHE_SHIFT))) > + break; > } > congestion_wait(WRITE, HZ/10); > }
I've been testing 2.6.23-rc9 + this patch all morning but have just seen a lockup. As usual it happened just after a large file copy finished and while nr_dirty is still large. I'm sorry to say I didn't have a serial console running so I don't have an other info. I will try again and see if I can capture some more data. I did notice that at the beginning of my tests the dirty blocks are written back more quickly than usual nr_dirty count after the copy finished and then 60 seconds later :- after copy +60 seconds 73520 0 73533 0 68554 1 but after several iterations of my testcase & just before the lockup 68560 57165 71974 62896 which is about the same as a unpatched kernel. Richard - 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/
