linux-kernel - Re: [x86 PAT PATCH 0/2] x86 PAT vm

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Date:	Tue, 03 Apr 2012 10:03:23 +0400
From:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
CC:	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Pallipadi Venkatesh <venki@...gle.com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Nick Piggin <npiggin@...nel.dk>
Subject: Re: [x86 PAT PATCH 0/2] x86 PAT vm_flag code refactoring

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...

>
> We can simplify the track/untrack pfn routines and can remove the
> dependency on vm_pgoff completely. Am appending a patch which does this
> and also modified your x86 PAT patch based on this. Can you please
> check and if you are ok, merge these bits with the rest of your patches.

Ok, I'll checks this.

>
> thanks,
> suresh
> ---
>
> Konstantin Khlebnikov (1):
>    mm, x86, PAT: rework linear pfn-mmap tracking
>
> Suresh Siddha (1):
>    x86, pat: remove the dependency on 'vm_pgoff' in track/untrack pfn
>      vma routines
>
>   arch/x86/mm/pat.c             |   38 ++++++++++++++++++++++++--------------
>   include/asm-generic/pgtable.h |    4 ++--
>   include/linux/mm.h            |   15 +--------------
>   mm/huge_memory.c              |    7 +++----
>   mm/memory.c                   |   15 ++++++++-------
>   5 files changed, 38 insertions(+), 41 deletions(-)
>

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