Messages in this thread | | | Date | Wed, 12 Aug 2009 10:31:41 -0400 | From | Rik van Riel <> | Subject | Re: [RFC] respect the referenced bit of KVM guest pages? |
| |
Wu Fengguang wrote: > On Fri, Aug 07, 2009 at 11:17:22AM +0800, KOSAKI Motohiro wrote: >>> Andrea Arcangeli wrote: >>> >>>> Likely we need a cut-off point, if we detect it takes more than X >>>> seconds to scan the whole active list, we start ignoring young bits, >>> We could just make this depend on the calculated inactive_ratio, >>> which depends on the size of the list. >>> >>> For small systems, it may make sense to make every accessed bit >>> count, because the working set will often approach the size of >>> memory. >>> >>> On very large systems, the working set may also approach the >>> size of memory, but the inactive list only contains a small >>> percentage of the pages, so there is enough space for everything. >>> >>> Say, if the inactive_ratio is 3 or less, make the accessed bit >>> on the active lists count. >> Sound reasonable. > > Yes, such kind of global measurements would be much better. > >> How do we confirm the idea correctness? > > In general the active list tends to grow large on under-scanned LRU. > I guess Rik is pretty familiar with typical inactive_ratio values of > the large memory systems and may even have some real numbers :) > >> Wu, your X focus switching benchmark is sufficient test? > > It is a major test case for memory tight desktop. Jeff presents > another interesting one for KVM, hehe. > > Anyway I collected the active/inactive list sizes, and the numbers > show that the inactive_ratio is roughly 1 when the LRU is scanned > actively and may go very high when it is under-scanned.
inactive_ratio is based on the zone (or cgroup) size.
For zones it is a fixed value, which is available in /proc/zoneinfo
-- All rights reversed.
| |