Feature: UKSM support

[drdeimos]

It's possible to add uksm monitoring charts?
https://github.com/dolohow/uksm

Like KSM but more effectivity

[ktsaou]

interesting!

If I understand this right, UKSM is an extension of KSM. It replaces the core algorithm of it, but everything else remains the same.

So, netdata already monitors it. Just enable KSM and UKSM and you will have charts like these:

[drdeimos]

It use another /sys directory for metrics but similar file names:

$ ll /sys/kernel/mm/uksm/
total 0
-rw-r--r-- 1 root root 4.0K Nov 12 03:58 abundant_threshold
-rw-r--r-- 1 root root 4.0K Nov 12 03:58 cpu_governor
-rw-r--r-- 1 root root 4.0K Nov 12 03:58 cpu_ratios
-r--r--r-- 1 root root 4.0K Nov 12 03:58 ema_per_page_time
-rw-r--r-- 1 root root 4.0K Nov 12 03:58 eval_intervals
-r--r--r-- 1 root root 4.0K Nov 12 03:58 full_scans
-r--r--r-- 1 root root 4.0K Nov 12 03:58 hash_strength
-rw-r--r-- 1 root root 4.0K Nov 12 03:58 max_cpu_percentage
-r--r--r-- 1 root root 4.0K Nov 12 03:56 pages_scanned
-r--r--r-- 1 root root 4.0K Nov 12 03:56 pages_shared
-r--r--r-- 1 root root 4.0K Nov 11 21:28 pages_sharing
-r--r--r-- 1 root root 4.0K Nov 12 03:56 pages_unshared
-rw-r--r-- 1 root root 4.0K Nov 12 03:58 run
-rw-r--r-- 1 root root 4.0K Nov 12 03:58 sleep_millisecs
-r--r--r-- 1 root root 4.0K Nov 12 03:58 sleep_times
-rw-r--r-- 1 root root 4.0K Nov 12 03:58 thrash_threshold

Can I just fix the path in the netdata config file?
Where exactly?

[ktsaou]

At netdata.conf:

[plugin:proc:/sys/kernel/mm/ksm]
	# /sys/kernel/mm/ksm/pages_shared = /sys/kernel/mm/ksm/pages_shared
	# /sys/kernel/mm/ksm/pages_sharing = /sys/kernel/mm/ksm/pages_sharing
	# /sys/kernel/mm/ksm/pages_unshared = /sys/kernel/mm/ksm/pages_unshared
	# /sys/kernel/mm/ksm/pages_volatile = /sys/kernel/mm/ksm/pages_volatile
	# /sys/kernel/mm/ksm/pages_to_scan = /sys/kernel/mm/ksm/pages_to_scan

uncomment them too.

[ktsaou]

If it works, I'll make netdata lookup for it.

[drdeimos]

Uncommented this section and set new paths for pages_shared, pages_sharing, pages_unshared.
pages_volatile and pages_to_scan set to wrong files because without it netdata does now show Memory Deduper menu and this metrics non exist in UKSM:

[plugin:proc:/sys/kernel/mm/ksm]
        /sys/kernel/mm/ksm/pages_shared = /sys/kernel/mm/uksm/pages_shared
        /sys/kernel/mm/ksm/pages_sharing = /sys/kernel/mm/uksm/pages_sharing
        /sys/kernel/mm/ksm/pages_unshared = /sys/kernel/mm/uksm/pages_unshared
        /sys/kernel/mm/ksm/pages_volatile = /sys/kernel/mm/uksm/thrash_threshold # WRONG
        /sys/kernel/mm/ksm/pages_to_scan = /sys/kernel/mm/uksm/pages_scanned #WRONG

and get this (see screenshot):

[drdeimos]

On screen shot i've get "Saved 47 Mb". But
/sys/kernel/mm/uksm/pages_sharing = 18080 pages.
18080 pages with PAGESIZE 4096 byte =~ 70 Mbyte saved
18080*4096/1024/1024 = 70.625

[ktsaou]

You have to subtract pages_shared to find the savings. sharing pages have reduced to shared, so their diff is the savings.

ok, I can make a PR with this...

[drdeimos]

On official website doc:

• pages_shared: how many pages has been mapped by different page table entries, i.e. shared by different processes.
• pages_sharing: this is roughly the number of redundant pages you have saved, with uksm.

[ktsaou]

I think the key here is the word "roughly".

The redundant pages (sharing) have been merged into a smaller set of pages (shared). So the actual savings is their difference.

So, If you have 1000 sharing into 500 shared, you have 50% savings.
But, if you have 1000 sharing into 10 shared, you have 99% savings.

[drdeimos]

Ok. Thank you

[ktsaou]

It seems I was wrong here.
Issue #3304 describes it in detail and PR #3318 fixes it.

[stale]

Currently netdata team doesn't have enough capacity to work on this issue. We will be more than glad to accept a pull request with a solution to problem described here. This issue will be closed after another 60 days of inactivity.

[cakrit]

Seems fixed. Please reopen if necessary.