From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Mosberger Date: Fri, 19 Jan 2001 01:43:44 +0000 Subject: Re: [Linux-ia64] CONFIG_IA64_PAGE_SIZE Message-Id: List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org >>>>> On Thu, 18 Jan 2001 12:43:06 -0800, Rich Altmaier 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