From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id F15A06B009D for ; Wed, 6 Jan 2010 21:51:00 -0500 (EST) Date: Thu, 7 Jan 2010 10:50:54 +0800 From: Wu Fengguang Subject: Re: [RFC][PATCH] vmalloc: simplify vread()/vwrite() Message-ID: <20100107025054.GA11252@localhost> References: <20100107012458.GA9073@localhost> <20100107103825.239ffcf9.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100107103825.239ffcf9.kamezawa.hiroyu@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: Andrew Morton , Tejun Heo , Ingo Molnar , Nick Piggin , Andi Kleen , Hugh Dickins , Christoph Lameter , Linux Memory Management List , LKML , "Huang, Ying" List-ID: On Thu, Jan 07, 2010 at 09:38:25AM +0800, KAMEZAWA Hiroyuki wrote: > On Thu, 7 Jan 2010 09:24:59 +0800 > Wu Fengguang wrote: > > > vread()/vwrite() is only called from kcore/kmem to access one page at > > a time. So the logic can be vastly simplified. > > > I recommend you to rename the function because safety of function is > changed and you can show what callers are influenced. OK. > > The changes are: > > - remove the vmlist walk and rely solely on vmalloc_to_page() > > - replace the VM_IOREMAP check with (page && page_is_ram(pfn)) > > > > The VM_IOREMAP check is introduced in commit d0107eb07320b for per-cpu > > alloc. Kame, would you double check if this change is OK for that > > purpose? > > > I think VM_IOREMAP is for avoiding access to device configuration area and > unexpected breakage in device. Then, VM_IOREMAP are should be skipped by > the caller. (My patch _just_ moves the avoidance of callers to vread()/vwrite()) "device configuration area" is not RAM, so testing of RAM would be able to skip them? > > > The page_is_ram() check is necessary because kmap_atomic() is not > > designed to work with non-RAM pages. > > > I think page_is_ram() is not a complete method...on x86, it just check > e820's memory range. checking VM_IOREMAP is better, I think. (double check) Not complete or not safe? EFI seems to not update e820 table by default. Ying, do you know why? > > Even for a RAM page, we don't own the page, and cannot assume it's a > > _PAGE_CACHE_WB page. So I wonder whether it's necessary to do another > > patch to call reserve_memtype() before kmap_atomic() to ensure cache > > consistency? > > > > TODO: update comments accordingly > > > > BTW, f->f_pos problem on 64bit machine still exists and this patch is still > hard to test. I stopped that because anyone doesn't show any interests. I'm using your patch :) I feel most inconfident on this patch, so submitted it for RFC first. I'll then submit a full patch series including your f_pos fix. > I have no objection to your direction. > > but please rewrite the function explanation as > "addr" should be page alinged and bufsize should be multiple of page size." > and change the function names. OK, I'll rename it to vread_page(). Thanks, Fengguang -- 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