From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752134Ab2DDEk4 (ORCPT <rfc822;w@1wt.eu>);
	Wed, 4 Apr 2012 00:40:56 -0400
Received: from mail-bk0-f46.google.com ([209.85.214.46]:62338 "EHLO
	mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1750936Ab2DDEkQ (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Wed, 4 Apr 2012 00:40:16 -0400
Message-ID: <4F7BD0AB.1000401@openvz.org>
Date: Wed, 04 Apr 2012 08:40:11 +0400
From: Konstantin Khlebnikov <khlebnikov@openvz.org>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.2) Gecko/20120217 Firefox/10.0.2 Iceape/2.7.2
MIME-Version: 1.0
To: Suresh Siddha <suresh.b.siddha@intel.com>
CC: "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Andi Kleen <andi@firstfloor.org>,
        Pallipadi Venkatesh <venki@google.com>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Nick Piggin <npiggin@kernel.dk>
Subject: Re: [x86 PAT PATCH 0/2] x86 PAT vm_flag code refactoring
References: <20120331170947.7773.46399.stgit@zurg>  <1333413969-30761-1-git-send-email-suresh.b.siddha@intel.com>  <4F7A92AB.5010809@openvz.org> <1333494871.12400.10.camel@sbsiddha-desk.sc.intel.com>
In-Reply-To: <1333494871.12400.10.camel@sbsiddha-desk.sc.intel.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Suresh Siddha wrote:
> On Tue, 2012-04-03 at 10:03 +0400, Konstantin Khlebnikov wrote:
>> Suresh Siddha wrote:
>>> Konstantin,
>>>
>>> On Sat, 2012-03-31 at 21:09 +0400, Konstantin Khlebnikov wrote:
>>>> v2: Do not use batched pfn reserving for single-page VMA. This is not optimal
>>>> and breaks something, because I see glitches on the screen with i915/drm driver.
>>>> With this version glitches are gone, and I see the same regions in
>>>> /sys/kernel/debug/x86/pat_memtype_list as before patch. So, please review this
>>>> carefully, probably I'm wrong somewhere, or I have triggered some hidden bug.
>>>
>>> Actually it is not a hidden bug. In the original code, we were setting
>>> VM_PFN_AT_MMAP only for remap_pfn_range() but not for the vm_insert_pfn().
>>> Also the value of 'vm_pgoff' depends on the driver/mmap_region() in the case of
>>> vm_insert_pfn(). But with your proposed code, you were setting
>>> the VM_PAT for the single-page VMA also and end-up using wrong vm_pgoff in
>>> untrack_pfn_vma().
>>
>> But I set correct vma->vm_pgoff together with VM_PAT. But, it shouldn't work if vma is expandable...
>>
>
> Also, I am not sure if we can override vm_pgoff in the fault handling
> path. For example, looking at unmap_mapping_range_tree() it does depend
> on the vm_pgoff value and it might break if we change the vm_pgoff in
> track_pfn_vma_new() (which gets called from vm_insert_pfn() as part of
> the i915_gem_fault()).

Yes, and we shouldn't change vma under mm->mmap_sem read-lock.

>
> thanks,
> suresh
>
>
>