Lamia Youseff
2007-Sep-12 08:34 UTC
[Xen-devel] limitation in the process address space size,
Hi ,
I am performing some experimentation with Xen paravirtualization impact
on computational workloads, when i observed a strange behavior of the
domains (dom0 with 256MB, but i did not verify it for domU yet).
As I request more pages to my process address space (through regular
malloc calls), Xen places a limitation on the process address space size
in real memory. Above this threshold, the process would swap like crazy,
and hurt the computational performance of my code. To be more specific,
my program pseudo code is shown below. My dom0 is allocated 256 MB at
initialization. I then run my code and measure its performance in
MFLOPS, as well as the swap activity as the process requests more memory.
I observed that when the process resident set size (pages in real
memory) reaches about 78.39 MB (or 20,070 pages), the process starts
swapping memory pages. I did not see the same performance degradation
when i allocate 756MB for dom0. This was not definitely the same
behavior I get from the native kernel on the same machine (I get no
performance degradation).
I will appreciate if some one can shed some light on this kernel
behavior for me. Please ask me if i don''t give enough details of the
problem here.
Thank you,
Lamia Youseff
while (){
malloc more X bytes;
fill new bytes with random numbers;
do some floating point operations, and measure performance;
measure swapped pages and RSS (resident set size);
}
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Keir Fraser
2007-Sep-12 08:37 UTC
Re: [Xen-devel] limitation in the process address space size,
On 12/9/07 09:34, "Lamia Youseff" <lyouseff@cs.ucsb.edu> wrote:> This was not definitely the same > behavior I get from the native kernel on the same machine (I get no > performance degradation).How much memory do you give the native kernel? -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Lamia Youseff
2007-Sep-12 08:57 UTC
Re: [Xen-devel] limitation in the process address space size,
The native kernel gets 2GB. Keir Fraser wrote:> > On 12/9/07 09:34, "Lamia Youseff" <lyouseff@cs.ucsb.edu> wrote: > > >> This was not definitely the same >> behavior I get from the native kernel on the same machine (I get no >> performance degradation). >> > > How much memory do you give the native kernel? > > -- Keir > >_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Keir Fraser
2007-Sep-12 08:59 UTC
Re: [Xen-devel] limitation in the process address space size,
Well then. You swap in the dom0 256MB case because dom0 has insufficient memory to efficiently support the heap size of your test application. Give dom0 2GB and you''ll see that it doesn''t swap either. -- Keir On 12/9/07 09:57, "Lamia Youseff" <lyouseff@cs.ucsb.edu> wrote:> The native kernel gets 2GB. > > Keir Fraser wrote: >> >> On 12/9/07 09:34, "Lamia Youseff" <lyouseff@cs.ucsb.edu> wrote: >> >> >>> This was not definitely the same >>> behavior I get from the native kernel on the same machine (I get no >>> performance degradation). >>> >> >> How much memory do you give the native kernel? >> >> -- Keir >> >>_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel