Zlatko Calusic wrote:
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!
Thanks!
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.
As I see, most likely reason of such imbalances is 'break' condition inside of shrink_lruvec().
So can try to disable it see what will happen.
But these numbers from your desktop actually doesn't proves this problem. Seems like difference
between zones is within the precision of this method. I don't know how to describe this precisely.
Probably irregularity between milestones also should be taken into the account to describe current
situation and quality of measurement.
Here current numbers from my 8Gb node. Main workload is a torrent client.
Node 0, zone DMA32
nr_inactive_anon 1
nr_active_anon 1494
nr_inactive_file 404028
nr_active_file 365525
nr_dirtied 855068
nr_written 854991
avg_age_inactive_anon: 64942528
avg_age_active_anon: 64942528
avg_age_inactive_file: 1281317
avg_age_active_file: 15813376
Node 0, zone Normal
nr_inactive_anon 376
nr_active_anon 13793
nr_inactive_file 542605
nr_active_file 542247
nr_dirtied 2746747
nr_written 2746266
avg_age_inactive_anon: 65064192
avg_age_active_anon: 65064192
avg_age_inactive_file: 1260611
avg_age_active_file: 8765240
So, here noticeable imbalance in ages of active file lru and nr_dirtied/nr_written.
I have no idea why, but torrent client uses syscall fadvise() which messes whole picture.
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