Re: [PATCH 01/45] writeback: reduce calls to global_page_state inbalance_dirty_pages()
From: Peter Zijlstra
Date: Sun Oct 11 2009 - 07:27:37 EST
On Sun, 2009-10-11 at 18:50 +0800, Wu Fengguang wrote:
>
> Sorry for the confusion, but I mean, filesystems have to limit
> nr_writeback (directly or indirectly via the block io queue),
> otherwise it either hit nr_dirty to 0 (with the loop), or let
> nr_writeback grow out of control (without the loop).
Doesn't this require the writeback queue to have a limit < dirty_thresh?
Or more specifically, for the bdi case:
bdi_dirty + bdi_writeback + bdi_unstable <= bdi_thresh
we require that the writeback queue be smaller than bdi_thresh, which
could be quite difficult, since bdi_thresh can easily be 0.
Without observing the bdi_thresh constraint we can have:
\Sum_(over bdis) writeback_queue_size
dirty pages outstanding, which could be significantly higher than
dirty_thresh.
Or am I confused again?
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