Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030478AbXALFTa (ORCPT ); Fri, 12 Jan 2007 00:19:30 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030480AbXALFTa (ORCPT ); Fri, 12 Jan 2007 00:19:30 -0500 Received: from smtp.osdl.org ([65.172.181.24]:33795 "EHLO smtp.osdl.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030478AbXALFT3 (ORCPT ); Fri, 12 Jan 2007 00:19:29 -0500 Date: Thu, 11 Jan 2007 21:18:52 -0800 (PST) From: Linus Torvalds To: Nick Piggin cc: Bill Davidsen , Andrew Morton , Hua Zhong , Hugh Dickins , linux-kernel@vger.kernel.org, hch@infradead.org, kenneth.w.chen@intel.com, mjt@tls.msk.ru Subject: Re: O_DIRECT question In-Reply-To: <45A714F8.6020600@yahoo.com.au> Message-ID: References: <6d6a94c50701101857v2af1e097xde69e592135e54ae@mail.gmail.com> <6d6a94c50701102150w4c3b46d0w6981267e2b873d37@mail.gmail.com> <20070110220603.f3685385.akpm@osdl.org> <6d6a94c50701102245g6afe6aacxfcb2136baee5cbfa@mail.gmail.com> <20070110225720.7a46e702.akpm@osdl.org> <45A5E1B2.2050908@yahoo.com.au> <6d6a94c50701102354l7ab41a3bp4761566204f1d992@mail.gmail.com> <45A5F157.9030001@yahoo.com.au> <45A6F70E.1050902@tmr.com> <45A70EF9.40408@yahoo.com.au> <45A714F8.6020600@yahoo.com.au> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1393 Lines: 31 On Fri, 12 Jan 2007, Nick Piggin wrote: > > Yeah *smallish* higher order allocations are fine, and we use them all the > time for things like stacks or networking. > > But Aubrey (who somehow got removed from the cc list) wants to do order 9 > allocations from userspace in his nommu environment. I'm just trying to be > realistic when I say that this isn't going to be robust and a userspace > solution is needed. I do agree that order-9 allocations simply is unlikely to work without some pre-allocation notion or some serious work at active de-fragmentation (and the page cache is likely to be the _least_ of the problems people will hit - slab and other kernel allocations are likely to be much much harder to handle, since you can't free them in quite as directed a manner). But for smallish-order (eg perhaps 3-4 possibly even more if you are careful in other places), the page cache limiter may well be a "good enough" solution in practice, especially if other allocations can be controlled by strict usage patterns (which is not realistic in a general- purpose kind of situation, but might be realistic in embedded). Linus - 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/