Re: [Linux-ia64] CONFIG_IA64_PAGE_SIZE

[Don Dugger <n0ano@valinux.com>]

Actually, the situation isn't quite this bad.  Turns out the kernel
stack and kernel register stack are both contained in the static
sized task structure.  The task structure has a minimum size of
32K so the per process memory for these structures is the same
for all page sizes from 4K to 32K.

What will change is the amount of unused space in the last page
of the user's data section, shared library data section, stack
section and register stack section.  Using the standard assumption
that half of the last page is wasted and also assuming that each
process only uses 1 shared library then going from 4K to 64K
increases this wasted space by 30K so your calculation becomes
30K * 4 * 1K = 120M.

On Thu, Jan 18, 2001 at 12:43:06PM -0800, Rich Altmaier wrote:
> I very much like larger page sizes for their performance boosts,
> typically the VM efficiency helps both code+data allocation and
> helps IO operation setup/teardown.
> 
> However be aware of one significant downside to larger page sizes,
> for workloads involving a large number of small processes.
> Suppose you fire up 1000 processes on a system, then the
> additional physical memory consumption is significant.
> I actually don't know the correct calculation but guesstimate
> that per-process data structures which increase in size
> include kernel stack, task struct, each shared lib data segment,
> user data segment.  If the pagesize is increased from 4K to 64K,
> then 4 such elements yield  60K*4*1000 processes = 240Mbyte.
> 
> Some customers do complain about this (and I tell them to buy
> more memory and enjoy the performance).
> Thanks, Rich
> 
> 
> >
> >
> > On Thu, Jan 18, 2001 at 09:55:32AM -0800, Broadfoot, KenX wrote:
> > >
> > > Anyone in the know,
> > >
> > > I am using a 16KB page size for my Lion systems.
> > >
> > > Under the help section of make menuconfig is says:
> > >
> > > 4KB   best for ia32
> > >
> > > 8KB   best for ia64
> > >
> > > 16KB  best for ia64
> > >
> > > 64KB  Not for Itanium
> > >
> > >
> > > I just want to know what is the gain or loss if I used 8KB instead of 16KB
> > > page size.
> > >
> > > Also why is the 64KB page size bad for Itanium?
> > >
> > > Thanks.
> > >
> > > --ken
> > >
> 
> 
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-- 
Don Dugger
"Censeo Toto nos in Kansa esse decisse." - D. Gale
n0ano@valinux.com
Ph: 303/938-9838