From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with ESMTP id 658B9900086 for ; Tue, 19 Apr 2011 06:21:29 -0400 (EDT) Date: Tue, 19 Apr 2011 09:30:59 +0100 From: Mel Gorman Subject: Re: [patch] mm/vmalloc: remove guard page from between vmap blocks Message-ID: <20110419083059.GA23041@csn.ul.ie> References: <20110414211441.GA1700@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20110414211441.GA1700@cmpxchg.org> Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: Andrew Morton , Nick Piggin , Dave Chinner , Hugh Dickins , Christoph Hellwig , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Thu, Apr 14, 2011 at 05:14:41PM -0400, Johannes Weiner wrote: > The vmap allocator is used to, among other things, allocate per-cpu > vmap blocks, where each vmap block is naturally aligned to its own > size. Obviously, leaving a guard page after each vmap area forbids > packing vmap blocks efficiently and can make the kernel run out of > possible vmap blocks long before overall vmap space is exhausted. > > The new interface to map a user-supplied page array into linear > vmalloc space (vm_map_ram) insists on allocating from a vmap block > (instead of falling back to a custom area) when the area size is below > a certain threshold. With heavy users of this interface (e.g. XFS) > and limited vmalloc space on 32-bit, vmap block exhaustion is a real > problem. > > Remove the guard page from the core vmap allocator. vmalloc and the > old vmap interface enforce a guard page on their own at a higher > level. > > Signed-off-by: Johannes Weiner > Cc: Nick Piggin > Cc: Dave Chinner > Cc: Mel Gorman > Cc: Hugh Dickins > Cc: Christoph Hellwig If necessary, the guard page could be reintroduced as a debugging-only option (CONFIG_DEBUG_PAGEALLOC?). Otherwise it seems reasonable. Acked-by: Mel Gorman -- Mel Gorman SUSE Labs -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org