From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [RFC] Reserve huge pages for reliable MAP_PRIVATE hugetlbfs mappings From: Andi Kleen References: <20080421183621.GA13100@csn.ul.ie> Date: Wed, 23 Apr 2008 15:55:10 +0200 In-Reply-To: <20080421183621.GA13100@csn.ul.ie> (Mel Gorman's message of "Mon, 21 Apr 2008 19:36:22 +0100") Message-ID: <87hcdsznep.fsf@basil.nowhere.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org Return-Path: To: Mel Gorman Cc: wli@holomorphy.com, agl@us.ibm.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: Mel Gorman writes: > MAP_SHARED mappings on hugetlbfs reserve huge pages at mmap() time. This is > so that all future faults will be guaranteed to succeed. Applications are not > expected to use mlock() as this can result in poor NUMA placement. > > MAP_PRIVATE mappings do not reserve pages. This can result in an application > being SIGKILLed later if a large page is not available at fault time. This > makes huge pages usage very ill-advised in some cases as the unexpected > application failure is intolerable. Forcing potential poor placement with > mlock() is not a great solution either. > > This patch reserves huge pages at mmap() time for MAP_PRIVATE mappings similar > to what happens for MAP_SHARED mappings. This will break all applications that mmap more hugetlbpages than they actually use. How do you know these don't exist? > Opinions? Seems like a risky interface change to me. -Andi -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org