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SubjectRe: [PATCH 00/17] per device dirty throttling -v7
> Latest version of the per bdi dirty throttling patches.
> Most of the changes since last time are little cleanups and more
> detail in the split out of the floating proportion into their
> own little lib.
> Patches are against 2.6.22-rc4-mm2
> A rollup of all this against 2.6.21 is available here:
> This patch-set passes the starve an USB stick test..

I've done some testing of several problem cases.

1) fuse writable mmap patches + bash_shared_mapping
2) writes in a setup involving a loop dev
a) ext3 over loop over ext3
b) ext3 over loop over fuse-passthrough over ext3
c) ext3 over loop over ntfs-3g

Without the patch, in all the cases I've seen deadlocks or long
stalls. With the patch, I could not reproduce this in any of the
cases. As predicted, the patch is performing well in this respect :)

2a is the simplest to reproduce (2.6.22, dual core, 1GB ram)

dd if=/dev/zero of=/tmp/p5 bs=1M seek=4999 count=1
mkfs.ext3 -F /tmp/p5
mkdir /tmp/m5
mount -oloop /tmp/p5 /tmp/m5
dd if=/dev/zero of=/tmp/m5/foo bs=1M count=4000

The second dd can stall for indefinite amounts of time. Kicking it
with sync can get it moving, but it relapses after some time.

Even with the per-device-throttling patch, case 2 shows an nr_dirty
elevated far above the 10% limit, reaching 40% or higher. I believe,
this is due to a missing balance_dirty_pages() call in the loop
device. And indeed the anomaly can be solved by adding this patch:

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