Messages in this thread | | | Date | Wed, 28 Jul 2010 10:04:07 +0800 | From | Wu Fengguang <> | Subject | Re: [PATCH 2/6] writeback: reduce calls to global_page_state in balance_dirty_pages() |
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> > The global threshold check is added in place of clip_bdi_dirty_limit() > > for safety and not intended as a behavior change. If ever leading to > > big behavior change and regression, that it would be indicating some > > too permissive per-bdi threshold calculation. > > > > Did you see the global dirty threshold get exceeded when writing to 2+ > > devices? Occasional small exceeding should be OK though. I tried the > > following debug patch and see no warnings when doing two concurrent cp > > over local disk and NFS. > Oops, sorry. I've misread the code. You're right. There shouldn't be a big > change in the behavior.
It does indicate a missing point in the changelog. The paragraph is updated to:
We now set and clear dirty_exceeded not only based on bdi dirty limits, but also on the global dirty limit. The global limit check is added in place of clip_bdi_dirty_limit() for safety and not intended as a behavior change. The bdi limits should be tight enough to keep all dirty pages under the global limit at most time; occasional small exceeding should be OK though. The change makes the logic more obvious: the global limit is the ultimate goal and shall be always imposed.
Thanks, Fengguang
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