From mboxrd@z Thu Jan 1 00:00:00 1970 From: William Lee Irwin III Date: Sat, 13 Mar 2004 05:49:10 +0000 Subject: Re: Hugetlbpages in very large memory machines....... Message-Id: <20040313054910.GA655@holomorphy.com> List-Id: References: <40528383.10305@sgi.com> <20040313034840.GF4638@wotan.suse.de> In-Reply-To: <20040313034840.GF4638@wotan.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Andi Kleen Cc: Ray Bryant , lse-tech@lists.sourceforge.net, "linux-ia64@vger.kernel.org" , linux-kernel@vger.kernel.org On Sat, Mar 13, 2004 at 04:48:40AM +0100, Andi Kleen wrote: > One drawback is that the out of memory handling is lot less nicer > than it was before - when you run out of hugepages you get SIGBUS > now instead of a ENOMEM from mmap. Maybe some prereservation would > make sense, but that would be somewhat harder. Alternatively > fall back to smaller pages if possible (I was told it isn't easily > possible on IA64) That's not entirely true. Whether it's feasible depends on how the MMU is used. The HPW (Hardware Pagetable Walker) and short mode of the VHPT insist upon pagesize being a per-region attribute, where regions are something like 60-bit areas of virtualspace, which is likely what they're referring to. The VHPT in long mode should be capable of arbitrary virtual placement (modulo alignment of course). -- wli