On Tue, Jul 14, 2015 at 09:31:32AM +0900, Sergey Senozhatsky wrote: > Hello Minchan, > > On (07/14/15 08:36), Minchan Kim wrote: > [..] > > > if [ `cat /sys/block/zram<id>/compact` -gt 10 ]; then > > > echo 1 > /sys/block/zram<id>/compact; > > > fi > > > > > > Up until now user space could not tell whether compaction > > > will result in any gain. > > > > First of all, thanks for the looking this. > > > > Question: > > > > What is motivation? > > IOW, did you see big overhead by user-triggered compaction? so, > > do you want to throttle it by userspace? > > It depends on 'big overhead' definition, of course. We don't care > that much when compaction is issued by the shrinker, because things > are getting bad and we can sacrifice performance. But user triggered > compaction on a I/O pressured device can needlessly slow things down, > especially now, when we drain ALMOST_FULL classes. You mean performance overhead by additional alloc_pages? If so, you mean ALMOST_EMPTY|ALMOST_FULL, not only ALMOST_FULL? So, it's performance enhance patch? Please give the some number to justify patchset. > > /sys/block/zram<id>/compact is a black box. We provide it, we don't > throttle it in the kernel, and user space is absolutely clueless when > it invokes compaction. From some remote (or alternative) point of But we have zs_can_compact so it can effectively skip the class if it is not proper class. > view compaction can be seen as "zsmalloc's cache flush" (unused objects > make write path quicker - no zspage allocation needed) and it won't > hurt to give user space some numbers so it can decide if the whole > thing is worth it (that decision is, once again, I/O pattern and > setup specific -- some users may be interested in compaction only > if it will reduce zsmalloc's memory consumption by, say, 15%). Again, your claim is performace so I need number. If it's really horrible, I guess below interface makes user handy without peeking nr_can_compact ad doing compact. /* Tell zram to compact if fragment ration is higher 15% */ echo 15% > /sys/block/zram0/compact or echo 15% > /sys/block/zram/compact_condition Anyway, we need a number before starting discussion. Thanks. > > -ss -- Kind regards, Minchan Kim -- 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>