Messages in this thread | | | Date | Thu, 30 Jul 2009 09:49:17 +0800 | From | Wu Fengguang <> | Subject | Re: Bug in kernel 2.6.31, Slow wb_kupdate writeout |
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On Thu, Jul 30, 2009 at 08:19:34AM +0800, Martin Bligh wrote: > BTW, can you explain this code at the bottom of generic_sync_sb_inodes > for me? > > if (wbc->nr_to_write <= 0) { > wbc->more_io = 1; > break; > } > > I don't understand why we are setting more_io here? AFAICS, more_io > means there's more stuff to write ... I would think we'd set this if > nr_to_write was > 0 ?
That's true: wbc.nr_to_write will always be set to MAX_WRITEBACK_PAGES by wb_writeback() before entering generic_sync_sb_inodes().
So wbc.nr_to_write <=0 indicates we are interrupted by the quota and should revisit generic_sync_sb_inodes() to check for more io (which will _normally_ find more dirty pages to write).
> Or just have the section below brought up above this > break check and do: > > if (!list_empty(&sb->s_more_io) || !list_empty(&sb->s_io)) > wbc->more_io = 1; > > Am I just misunderstanding the intent of more_io ?
It should be OK. I agree on the change if it makes the logic more straightforward.
Thanks, Fengguang
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