From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id 692A46B005A for ; Fri, 1 May 2009 10:09:28 -0400 (EDT) Received: from localhost (smtp.ultrahosting.com [127.0.0.1]) by smtp.ultrahosting.com (Postfix) with ESMTP id 3FAC482C486 for ; Fri, 1 May 2009 10:21:00 -0400 (EDT) Received: from smtp.ultrahosting.com ([74.213.174.254]) by localhost (smtp.ultrahosting.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id ypad9vsdZYaj for ; Fri, 1 May 2009 10:21:00 -0400 (EDT) Received: from qirst.com (unknown [74.213.171.31]) by smtp.ultrahosting.com (Postfix) with ESMTP id 0B76182C541 for ; Fri, 1 May 2009 10:20:54 -0400 (EDT) Date: Fri, 1 May 2009 09:59:35 -0400 (EDT) From: Christoph Lameter Subject: Re: [PATCH mmotm] mm: alloc_large_system_hash check order In-Reply-To: <20090501140015.GA27831@csn.ul.ie> Message-ID: References: <20090430132544.GB21997@csn.ul.ie> <20090501140015.GA27831@csn.ul.ie> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: Mel Gorman Cc: Hugh Dickins , Andrew Morton , Andi Kleen , David Miller , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Fri, 1 May 2009, Mel Gorman wrote: > > Andrew noticed another oddity: that if it goes the hashdist __vmalloc() > > way, it won't be limited by MAX_ORDER. Makes one wonder whether it > > ought to fall back to __vmalloc() if the alloc_pages_exact() fails. > > I don't believe so. __vmalloc() is only used when hashdist= is used or on IA-64 > (according to the documentation). It is used in the case that the caller is > willing to deal with the vmalloc() overhead (e.g. using base page PTEs) in > exchange for the pages being interleaved on different nodes so that access > to the hash table has average performance[*] > > If we automatically fell back to vmalloc(), I bet 2c we'd eventually get > a mysterious performance regression report for a workload that depended on > the hash tables performance but that there was enough memory for the hash > table to be allocated with vmalloc() instead of alloc_pages_exact(). Can we fall back to a huge page mapped vmalloc? Like what the vmemmap code does? Then we also would not have MAX_ORDER limitations. -- 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