On Thu, 11 Jan 2007 14:35:06 -0800 (PST) dean gaudet <[EMAIL PROTECTED]> 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 [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/