On 01/13/2017 08:14 AM, js1304@xxxxxxxxx wrote: > From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > > Until now, we invoke the compaction whenever allocation request is stall > due to non-existence of the high order freepage. It is effective since we > don't need a high order freepage in usual and cost of maintaining > high order freepages is quite high. However, it increases latency of high > order allocation request and decreases success rate if allocation request > cannot use the reclaim/compaction. Since there are some workloads that > require high order freepage to boost the performance, it is a matter of > trade-off that we prepares high order freepage in advance. Now, there is > no way to prepare high order freepages, we cannot consider this trade-off. > Therefore, this patch introduces a way to invoke the compaction when > necessary to manage trade-off. > > Implementation is so simple. There is a theshold to invoke the full > compaction. If fragmentation ratio reaches this threshold in given order, > we ask the full compaction to kcompactd with a hope that it restores > fragmentation ratio. > > If fragmentation ratio is unchanged or worse after full compaction, > further compaction attempt would not be useful. So, this patch > stops the full compaction in this case until the situation changes > to avoid useless compaction effort. > > Now, there is no scientific code to detect the situation change. > kcompactd's full compaction would be re-enabled when lower order > triggers kcompactd wake-up or time limit (a second) is passed. > > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> So, as you expected, I'm not thrilled about the tunables :) And also the wakeups from allocator hotpaths. Otherwise I'll wait with discussing details until we get some consensus on usecases and metrics. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>