Re: [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:
  http://programming.kicks-ass.net/kernel-patches/balance_dirty_pages/2.6.21-per_bdi_dirty_pages.patch

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:

  http://lkml.org/lkml/2007/3/24/101

Miklos

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