(removed lsf-pc@lists.linux-foundation.org because this really isn't
program committee matter)

On Wed, Feb 1, 2012 at 11:52 PM, Wu Fengguang [off-list ref] wrote:

Unfortunately the memcg partitioning could fundamentally make the
dirty throttling more bumpy.

Imagine 10 memcgs each with

- memcg_dirty_limit=50MB
- 1 dd dirty task

The flusher thread will be working on 10 inodes in turn, each time
grabbing the next inode and taking ~0.5s to write ~50MB of its dirty
pages to the disk. So each inode will be flushed on every ~5s.

Does the flusher thread need to write 50MB/inode in this case?  Would
there be problems interleaving writes by declaring some max write
limit (e.g. 8 MiB/write).  Such interleaving would be beneficial if
there are multiple memcg expecting service from the single bdi flusher
thread.  I suspect certain filesystems might have increased
fragmentation with this, but I am not sure if appending writes can
easily expand an extent.

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