Guest JÅns MÁrtin SchlÁttÅr Posted September 23, 2008 Posted September 23, 2008 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 Posted September 23, 2008 Posted September 23, 2008 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 Posted September 23, 2008 Posted September 23, 2008 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 Posted September 23, 2008 Posted September 23, 2008 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 Posted September 23, 2008 Posted September 23, 2008 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 Posted September 23, 2008 Posted September 23, 2008 Re: sort causes page faults on server machine thanks for your perfect answer!
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