Re: [Linux-ia64] CONFIG_IA64_PAGE_SIZE

David Mosberger
2001-01-19T01:43:44Z

>>>>> On Thu, 18 Jan 2001 12:43:06 -0800, Rich Altmaier <richa@engr.sgi.com> said:

Rich> However be aware of one significant downside to larger page
Rich> sizes, for workloads involving a large number of small
Rich> processes. Suppose you fire up 1000 processes on a system,
Rich> then the additional physical memory consumption is
Rich> significant. I actually don't know the correct calculation
Rich> but guesstimate that per-process data structures which
Rich> increase in size include kernel stack, task struct, each
Rich> shared lib data segment, user data segment. If the pagesize
Rich> is increased from 4K to 64K, then 4 such elements yield
Rich> 60K*4*1000 processes = 240Mbyte.

The minimum task size was an important consideration in the design of
IA-64 Linux. As Don pointed out, the process data structure is at
least 32KB no matter what page size is in use (to avoid stack
overflow), so this really makes a difference only when the page size
is 64KB.

However, the real biggie are the page tables. Even the smallest task
needs at the least three page table pages, so here the page size can
have a big impact.

Rich> Some customers do complain about this (and I tell them to buy
Rich> more memory and enjoy the performance).

Good answer! ;-)

--david