Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759455AbXFTIHF (ORCPT ); Wed, 20 Jun 2007 04:07:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1761117AbXFTIGt (ORCPT ); Wed, 20 Jun 2007 04:06:49 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:38212 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757385AbXFTIGs (ORCPT ); Wed, 20 Jun 2007 04:06:48 -0400 Subject: Re: [Intel IOMMU 06/10] Avoid memory allocation failures in dma map api calls From: Peter Zijlstra To: "Keshavamurthy, Anil S" Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, ak@suse.de, gregkh@suse.de, muli@il.ibm.com, suresh.b.siddha@intel.com, arjan@linux.intel.com, ashok.raj@intel.com, davem@davemloft.net, clameter@sgi.com In-Reply-To: <20070619213808.798646000@askeshav-devel.jf.intel.com> References: <20070619213701.219910000@askeshav-devel.jf.intel.com> <20070619213808.798646000@askeshav-devel.jf.intel.com> Content-Type: text/plain Date: Wed, 20 Jun 2007 10:06:39 +0200 Message-Id: <1182326799.21117.19.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.10.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2035 Lines: 45 On Tue, 2007-06-19 at 14:37 -0700, Keshavamurthy, Anil S wrote: > plain text document attachment (intel_iommu_pf_memalloc.patch) > Intel IOMMU driver needs memory during DMA map calls to setup its internal > page tables and for other data structures. As we all know that these DMA > map calls are mostly called in the interrupt context or with the spinlock > held by the upper level drivers(network/storage drivers), so in order to > avoid any memory allocation failure due to low memory issues, > this patch makes memory allocation by temporarily setting PF_MEMALLOC > flags for the current task before making memory allocation calls. > > We evaluated mempools as a backup when kmem_cache_alloc() fails > and found that mempools are really not useful here because > 1) We don;t know for sure how much to reserve in advance So you just unleashed an unbounded allocation context on PF_MEMALLOC? seems like a really really bad idea. > 2) And mempools are not useful for GFP_ATOMIC case (as we call > memory alloc functions with GFP_ATOMIC) Mempools work as intended with GFP_ATOMIC, it gets filled up to the specified number of elements using GFP_KERNEL (at creation time). This gives GFP_ATOMIC allocations nr_elements extra items once it would start failing. > With PF_MEMALLOC flag set in the current->flags, the VM subsystem avoids > any watermark checks before allocating memory thus guarantee'ing the > memory till the last free page. PF_MEMALLOC as is, is meant to salvage the VM from the typical VM deadlock. Using it as you do now is not something a driver should ever do, and I'm afraid I will have to strongly oppose this patch. You really really want to calculate an upper bound on your memory consumption and reserve this. So, I'm afraid I'll have to.. NACK! - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/