On 06/21/2012 02:52 AM, David Rientjes wrote:

If page migration cannot charge the new page to the memcg,
migrate_pages() will return -ENOMEM.  This isn't considered in memory
compaction however, and the loop continues to iterate over all pageblocks
trying in a futile attempt to continue migrations which are only bound to
fail.

This will short circuit and fail memory compaction if migrate_pages()
returns -ENOMEM.  COMPACT_PARTIAL is returned in case some migrations
were successful so that the page allocator will retry.

The patch makes sense, however I wonder if it would make
more sense in the long run to allow migrate/compaction to
temporarily exceed the memcg memory limit for a cgroup,
because the original page will get freed again soon anyway.

That has the potential to improve compaction success, and
reduce compaction related CPU use.

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