sort causes page faults on server machine

[Guest JÅns MÁrtin SchlÁttÅr]

We have a win 2003 server which is accessed by multiple clients

(around 10) by RDP.

The machine has 4GB memory.

When we start a SAS sort, the performance monitor shows a lot of page

faults, but the machine has still 2GB memory available.

 

Why does a process experience page faults when there is plenty of

memory free?

 

Martin

[Guest RolandRB]

Re: sort causes page faults on server machine

 

On Sep 23, 2:46špm, "JÅns MÁrtin SchlÁttÅr"

<KmoEfrUew...@spammotel.com> wrote:

> We have a win 2003 server which is accessed by multiple clients

> (around 10) by RDP.

> The machine has 4GB memory.

> When we start a SAS sort, the performance monitor shows a lot of page

> faults, but the machine has still 2GB memory available.

>

> Why does a process experience page faults when there is plenty of

> memory free?

>

> Martin

 

Because the overall physical memory allowance for the sas job is less

than it needs. There must be a way of changing your limit but this

might have to be negotiated with the systems people.

[Guest Jeff Pitsch]

Re: sort causes page faults on server machine

 

If the file(s) are read-only to begin with and a user does something

that writes to that memory location, windows will fault and write a copy

of the orginal file to the page file and then create a read/write copy

in memory. So if during this sort process, many files are manipulated

in memory then you could see this behavior. My suggestion would be to

contact the vendor and ask them what is going on in their product to

cause the page faults.

 

Jeff Pitsch

Microsoft MVP - Terminal Services

 

J?ns M?rtin Schl?tt?r wrote:

> We have a win 2003 server which is accessed by multiple clients

> (around 10) by RDP.

> The machine has 4GB memory.

> When we start a SAS sort, the performance monitor shows a lot of page

> faults, but the machine has still 2GB memory available.

>

> Why does a process experience page faults when there is plenty of

> memory free?

>

> Martin

>

[Guest jolteroli]

Re: sort causes page faults on server machine

 

nothing to wonder about Martin. if an application commits some memory --

which obviously is a must for sorting -- the page-tables will be created but

tagged as non-present. that means the memory is mapped in virtual memory but

doesn't point to any physical memory.

 

if the application now accesses (r/w) one of this non-present pages, the

processor generates an exception (14) and calls the os page fault handler.

this handler now, will allocate a physical memory page and setup the

page-table-entry that it points to this physical page. on the handler

return, the causing instruction will be restarted and the memory access will

succeed.

 

since the os keeps tracks of various page-fault-counters, you will see this

on-demand-allocation in a raising number of page faults.

 

the background is that most programmers do over-commits. instead to geting

the file size and allocating exactly this amount of memory, they e.g. alloc

1MB memory to read in a 3k configuration file. with this on demapand

allocation, the system will only give away that much physical memory to the

process, as the application has touched and the remeaning memory can used

for caching still.

 

-jolt

 

 

"J?ns M?rtin Schl?tt?r" <KmoEfrUewEbx@spammotel.com> schrieb im Newsbeitrag

news:vImTVl25inkn-pn2-r0B5DztOIJrQ@registered.motzarella.org...

> We have a win 2003 server which is accessed by multiple clients

> (around 10) by RDP.

> The machine has 4GB memory.

> When we start a SAS sort, the performance monitor shows a lot of page

> faults, but the machine has still 2GB memory available.

>

> Why does a process experience page faults when there is plenty of

> memory free?

>

> Martin

>

[Guest jolteroli]

Re: sort causes page faults on server machine

 

nothing to wonder about Martin. if an application commits some memory --

which obviously is a must for sorting -- the page-tables will be created but

tagged as non-present. that means the memory is mapped in virtual memory but

doesn't point to any physical memory.

 

if the application now accesses (r/w) one of this non-present pages, the

processor generates an exception (14) and calls the os page fault handler.

this handler now, will allocate a physical memory page and setup the

page-table-entry that it points to this physical page. on the handler

return, the causing instruction will be restarted and the memory access will

succeed.

 

since the os keeps tracks of various page-fault-counters, you will see this

on-demand-allocation in a raising number of page faults.

 

the background is that most programmers do over-commits. instead to geting

the file size and allocating exactly this amount of memory, they e.g. alloc

1MB memory to read in a 3k configuration file. with this on demapand

allocation, the system will only give away that much physical memory to the

process, as the application has touched and the remeaning memory can used

for caching still.

 

-jolt

 

 

"J?ns M?rtin Schl?tt?r" <KmoEfrUewEbx@spammotel.com> schrieb im Newsbeitrag

news:vImTVl25inkn-pn2-r0B5DztOIJrQ@registered.motzarella.org...

> We have a win 2003 server which is accessed by multiple clients

> (around 10) by RDP.

> The machine has 4GB memory.

> When we start a SAS sort, the performance monitor shows a lot of page

> faults, but the machine has still 2GB memory available.

>

> Why does a process experience page faults when there is plenty of

> memory free?

>

> Martin

>

[Guest JÅns MÁrtin SchlÁttÅr]

Re: sort causes page faults on server machine

 

thanks for your perfect answer!