From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx132.postini.com [74.125.245.132]) by kanga.kvack.org (Postfix) with SMTP id 353886B002C for ; Wed, 8 Feb 2012 15:58:01 -0500 (EST) Received: by qcsd16 with SMTP id d16so692922qcs.14 for ; Wed, 08 Feb 2012 12:58:00 -0800 (PST) Message-ID: <4F32E1D2.4010809@vflare.org> Date: Wed, 08 Feb 2012 15:57:54 -0500 From: Nitin Gupta MIME-Version: 1.0 Subject: Re: [PATCH 1/5] staging: zsmalloc: zsmalloc memory allocation library References: <1326149520-31720-1-git-send-email-sjenning@linux.vnet.ibm.com> <1326149520-31720-2-git-send-email-sjenning@linux.vnet.ibm.com> <4F21A5AF.6010605@linux.vnet.ibm.com> <4F300D41.5050105@linux.vnet.ibm.com> <4F32A55E.8010401@linux.vnet.ibm.com> <4F32B6A4.8030702@vflare.org> <4F32BEDC.6030502@linux.vnet.ibm.com> In-Reply-To: <4F32BEDC.6030502@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: Seth Jennings , Greg Kroah-Hartman , Dan Magenheimer , Brian King , Konrad Wilk , linux-mm@kvack.org, devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org On 02/08/2012 01:28 PM, Dave Hansen wrote: > On 02/08/2012 09:53 AM, Nitin Gupta wrote: >> vmap() is not just slower but also does memory allocations at various >> places. Under memory pressure, this may cause failure in reading a >> stored object just because we failed to map it. Also, it allocates VA >> region each time its called which is a real big waste when we can simply >> pre-allocate 2 * PAGE_SIZE'ed VA regions (per-cpu). > > Yeah, vmap() is a bit heavy-handed. I'm just loathe to go mucking > around in the low-level pagetables too much. Just seems like there'll > be a ton of pitfalls, like arch-specific TLB flushing, and it _seems_ > like one of the existing kernel mechanisms should work. > > I guess if you've exhaustively explored all of the existing kernel > mapping mechanisms and found none of them to work, and none of them to > be in any way suitably adaptable to your use, you should go ahead and > roll your own. I guess you do at least use alloc_vm_area(). What made > map_vm_area() unsuitable for your needs? If you're remapping, you > should at least be guaranteed not to have to allocate pte pages. > map_vm_area() needs 'struct vm_struct' parameter but for mapping kernel allocated pages within kernel, what should we pass here? I think we can instead use map_kernel_range_noflush() -- surprisingly unmap_kernel_range_noflush() is exported but this one is not. Nitin -- 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