Re: [patch] mm, thp: abort compaction if migration page cannot be charged to memcg

Rik van Riel
2012-06-25T20:41:57Z

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.