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Vmstat

 

Vmstat

Hi Admins.

i am working with vmstat output of few systems,

i want to understand the "sr" column in vmstat output. and it's significance in performance determination.

Pls help out.
Thanx in Advance

Sandeep



6 REPLIES
Ivan Krastev
Honored Contributor

Re: Vmstat

Re: Vmstat

vmstat(1) says:
sr Pages scanned by clock algorithm, per second

I assume this means it has to look at lots of pages in order to find the pages to swap out to make room?

Re: Vmstat

Hi Dennis,

Do you mean to say high scan rates indicates,shortage of swap memmory.
and i will be seeing swap utilization approaching to it's full capacity.in swapinfo at that time.

Sandeep

Re: Vmstat

>Do you mean to say high scan rates indicates, shortage of swap memory?

No, a shortage of RAM, memory pressure.

Re: Vmstat

Hi Dennins,

Thnks for reply

I meant shortage of swap only.

according to me,
Since "sr" in vmstat is scan rate by memory manager ( page replacement algorithm as mentioned in man page ) to lookfor free pages in swap.and if this scanning more to find a free swap page. it indicates that real memory as well as swap is also falling in shortage.

so what i meant is swap shortage with RAM shortage. so in t his case in swapinfo i may see swap utilization approaching it's capacity.

this is what i feel.

i just want ensure my conclusion from experts.

Pls. correct me if i m wrong.

Sandeep

Re: Vmstat

>I meant shortage of swap only.

No, it doesn't take a lot of time to allocate swap. It is too small to be worth measuring.

>Since "sr" in vmstat is scan rate by memory manager to look for free pages in swap

No, the memory manager looks for pages in memory.

>if this scanning more to find a free swap page. it indicates that real memory as well as swap is also falling in shortage.

A free page to page out.

>so what I meant is swap shortage with RAM shortage. so in this case in swapinfo I may see swap utilization approaching its capacity.

This is unrelated to sr.