On 04/09/2019 01:01, Mark Johnston wrote: > Slawa and I talked about this in the past. His complaint is that a > large cache can take a significant amount of time to trim, and it > manifests as a spike of CPU usage and contention on the zone lock. In > particular, keg_drain() iterates over the list of free slabs with the > keg lock held, and if the many items were freed to the keg while > trimming/draining, the list can be quite long. This can have effects > outside the zone, for example if we are reclaiming items from zones used > by other UMA zones, like the bucket or slab zones.
My concern is different, though. I feel that having oversized caches for long periods of time produces a skewed picture of memory usage. Particularly, some ZFS caches are sometimes extremely oversized. I don't care much about details of consequences of such oversized caches. I just think that that is not right on a more general level. > Reclaiming cached items when there is no demand for free pages seems > wrong to me. It certainly was wrong before. Now that we have a capability to trim a cache size to a workset size it doesn't feel as wrong to me. > We historically had similar problems with the page daemon, > which last year was changed to perform smaller reclamations at a greater > frequency. I suspect a better approach for UMA would be to similarly > increase reclaim frequency and reduce the number of items freed in one > go. -- Andriy Gapon _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
