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

Minchan Kim
2012-06-21T08:11:35Z

On 06/21/2012 03:52 PM, 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.

Hmm, it might be dumb question.
I imagine that pages in next pageblock could be in another memcg so it could be successful.
Why should we stop compaction once it fails to migrate pages in current pageblock/memcg?

>
> 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.
>
> Signed-off-by: David Rientjes <rientjes@google.com>
> ---
> mm/compaction.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -701,8 +701,11 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
> if (err) {
> putback_lru_pages(&cc->migratepages);
> cc->nr_migratepages = 0;
> + if (err == -ENOMEM) {
> + ret = COMPACT_PARTIAL;
> + goto out;
> + }
> }
> -
> }
>
> out:

--
Kind regards,
Minchan Kim