Messages in this thread | | | Date | Thu, 11 Jan 2007 14:48:01 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH - RFC] allow setting vm_dirty below 1% for large memory machines |
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On Thu, 11 Jan 2007 14:35:06 -0800 (PST) dean gaudet <dean@arctic.org> wrote:
> actually a global dirty_ratio causes interference between devices which > should otherwise not block each other... > > if you set up a "dd if=/dev/zero of=/dev/sdb bs=1M" it shouldn't affect > write performance on sda -- but it does... because the dd basically > dirties all of the "dirty_background_ratio" pages and then any task > writing to sda has to block in the foreground... (i've had this happen in > practice -- my hack fix is oflag=direct on the dd... but the problem still > exists.)
yeah. Plus your heavy-dd-to-/dev/sda tends to block light-writers to /dev/sda in perhaps disproportionate ways.
This is on my list of things to look at. Hah.
> i'm not saying fixing any of this is easy, i'm just being a user griping > about it :)
It's rather complex, I believe. Needs per-backing-dev dirty counts (already in -mm) plus, I suspect, per-process dirty counts (possibly derivable from per-task-io-accounting) plus some tricky logic to make all that work along with global dirtiness (and later per-node dirtiness!) while meeting all the constraints which that logic must satisfy. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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