Hello Minchan, On (03/14/16 15:17), Minchan Kim wrote: [..] > > demonstrates that class-896 has 12/26=46% of unused pages, class-2336 has > > 1648/4932=33% of unused pages, etc. And the more classes we will have as > > 'normal' classes (more than one object per-zspage) the bigger this problem > > will grow. The existing compaction relies on a user space (user can trigger > > compaction via `compact' zram's sysfs attr) or a shrinker; it does not > > happen automatically. > > > > This patch introduces a 'watermark' value of unused pages and schedules a > > compaction work on a per-class basis once class's fragmentation becomes > > too big. So compaction is not performed in current I/O operation context, > > but in workqueue workers later. > > > > The current watermark is set to 40% -- if class has 40+% of `freeable' > > pages then compaction work will be scheduled. > > Could you explain why you select per-class watermark? yes, we do less work this way - scan and compact only one class, instead of locking and compacting all of them; which sounds reasonable. > Because my plan was we kick background work based on total fragmented memory > (i.e., considering used_pages/allocated_pages < some threshold). if we know that a particular class B is fragmented and the rest of them are just fine, then we can compact only that class B, skipping extra job. > IOW, if used_pages/allocated_pages is less than some ratio, > we kick background job with marking index of size class just freed > and then the job scans size_class from the index circulary. > > As well, we should put a upper bound to scan zspages to make it > deterministic. you mean that __zs_compact() instead of just checking per-class zs_can_compact() should check global pool ratio and bail out if compaction of class Z has dropped the overall fragmentation ratio below some watermark? my logic was that -- suppose we have class A with fragmentation ratio 49% and class B with 8% of wasted pages, so the overall pool fragmentation is (50 + 10)/ 2 < 30%, while we still have almost 50% fragmented class. if the aim is to reduce the memory wastage then per-class watermarks seem to be more flexible. > What do you think about it? -ss -- 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>