On 30.04.2013 13:02, Konstantin Khlebnikov wrote:
This patch adds engine for estimating rotation time for pages in lru lists.
This adds bunch of 'milestones' into each struct lruvec and inserts them into
lru lists periodically. Milestone flows in lru together with pages and brings
timestamp to the end of lru. Because milestones are embedded into lruvec they
can be easily distinguished from pages by comparing pointers.
Only few functions should care about that.
This machinery provides discrete-time estimation for age of pages from the end
of each lru and average age of each kind of evictable lrus in each zone.
Great stuff!
Believe it or not, I had an idea of writing something similar to this,
but of course having an idea and actually implementing it are two very
different things. Thank you for your work!
I will use this to prove (or not) that file pages in the normal zone on
a 4GB RAM machine are reused waaaay too soon. Actually, I already have
the patch applied and running on the desktop, but it should be much more
useful on server workloads. Desktops have erratic load and can go for a
long time with very little I/O activity. But, here are the current
numbers anyway:
Node 0, zone DMA32
pages free 5371
nr_inactive_anon 4257
nr_active_anon 139719
nr_inactive_file 617537
nr_active_file 51671
inactive_ratio: 5
avg_age_inactive_anon: 2514752
avg_age_active_anon: 2514752
avg_age_inactive_file: 876416
avg_age_active_file: 2514752
Node 0, zone Normal
pages free 424
nr_inactive_anon 253
nr_active_anon 54480
nr_inactive_file 63274
nr_active_file 44116
inactive_ratio: 1
avg_age_inactive_anon: 2531712
avg_age_active_anon: 2531712
avg_age_inactive_file: 901120
avg_age_active_file: 2531712
In our kernel we use similar engine as source of statistics for scheduler in
memory reclaimer. This is O(1) scheduler which shifts vmscan priorities for lru
vectors depending on their sizes, limits and ages. It tries to balance memory
pressure among containers. I'll try to rework it for the mainline kernel soon.
Seems like these ages also can be used for optimal memory pressure distribution
between file and anon pages, and probably for balancing pressure among zones.
This all sounds very promising. Especially because I currently observe
quite some imbalance among zones.
Regards,
--
Zlatko
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