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Subject: Re: [PATCH v5 05/15] mm/frame-vector: Use FOLL_LONGTERM
To:     Jason Gunthorpe <jgg@ziepe.ca>,
        Christoph Hellwig <hch@infradead.org>,
        J??r??me Glisse <jglisse@redhat.com>,
        linux-samsung-soc <linux-samsung-soc@vger.kernel.org>,
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References: <CAKMK7uEw701AWXNJbRNM8Z+FkyUB5FbWegmSzyWPy9cG4W7OLA@mail.gmail.com>
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 <20201104163758.GA17425@infradead.org> <20201104164119.GA18218@infradead.org>
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From:   John Hubbard <jhubbard@nvidia.com>
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On 11/5/20 4:49 AM, Jason Gunthorpe wrote:
> On Thu, Nov 05, 2020 at 10:25:24AM +0100, Daniel Vetter wrote:
>>> /*
>>>   * If we can't determine whether or not a pte is special, then fail immediately
>>>   * for ptes. Note, we can still pin HugeTLB and THP as these are guaranteed not
>>>   * to be special.
>>>   *
>>>   * For a futex to be placed on a THP tail page, get_futex_key requires a
>>>   * get_user_pages_fast_only implementation that can pin pages. Thus it's still
>>>   * useful to have gup_huge_pmd even if we can't operate on ptes.
>>>   */
>>
>> We support hugepage faults in gpu drivers since recently, and I'm not
>> seeing a pud_mkhugespecial anywhere. So not sure this works, but probably
>> just me missing something again.
> 
> It means ioremap can't create an IO page PUD, it has to be broken up.
> 
> Does ioremap even create anything larger than PTEs?
> 

 From my reading, yes. See ioremap_try_huge_pmd().

thanks,
-- 
John Hubbard
NVIDIA

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Subject: Re: [PATCH v5 05/15] mm/frame-vector: Use FOLL_LONGTERM
To: Jason Gunthorpe <jgg@ziepe.ca>, Christoph Hellwig <hch@infradead.org>,
	J??r??me Glisse <jglisse@redhat.com>, linux-samsung-soc
	<linux-samsung-soc@vger.kernel.org>, Jan Kara <jack@suse.cz>, Pawel Osciak
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	<dan.j.williams@intel.com>, Linux ARM <linux-arm-kernel@lists.infradead.org>,
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References: <CAKMK7uEw701AWXNJbRNM8Z+FkyUB5FbWegmSzyWPy9cG4W7OLA@mail.gmail.com>
 <20201104140023.GQ36674@ziepe.ca>
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 <CAKMK7uH=0+3FSR4LxP7bJUB4BsCcnCzfK2=D+2Am9QNmfZEmfw@mail.gmail.com>
 <20201104163758.GA17425@infradead.org> <20201104164119.GA18218@infradead.org>
 <20201104181708.GU36674@ziepe.ca>
 <d3497583-2338-596e-c764-8c571b7d22cf@nvidia.com>
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From: John Hubbard <jhubbard@nvidia.com>
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On 11/5/20 4:49 AM, Jason Gunthorpe wrote:
> On Thu, Nov 05, 2020 at 10:25:24AM +0100, Daniel Vetter wrote:
>>> /*
>>>   * If we can't determine whether or not a pte is special, then fail immediately
>>>   * for ptes. Note, we can still pin HugeTLB and THP as these are guaranteed not
>>>   * to be special.
>>>   *
>>>   * For a futex to be placed on a THP tail page, get_futex_key requires a
>>>   * get_user_pages_fast_only implementation that can pin pages. Thus it's still
>>>   * useful to have gup_huge_pmd even if we can't operate on ptes.
>>>   */
>>
>> We support hugepage faults in gpu drivers since recently, and I'm not
>> seeing a pud_mkhugespecial anywhere. So not sure this works, but probably
>> just me missing something again.
> 
> It means ioremap can't create an IO page PUD, it has to be broken up.
> 
> Does ioremap even create anything larger than PTEs?
> 

 From my reading, yes. See ioremap_try_huge_pmd().

thanks,
-- 
John Hubbard
NVIDIA


From mboxrd@z Thu Jan  1 00:00:00 1970
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Subject: Re: [PATCH v5 05/15] mm/frame-vector: Use FOLL_LONGTERM
To: Jason Gunthorpe <jgg@ziepe.ca>, Christoph Hellwig <hch@infradead.org>,
 J??r??me Glisse <jglisse@redhat.com>, linux-samsung-soc
 <linux-samsung-soc@vger.kernel.org>, Jan Kara <jack@suse.cz>, Pawel Osciak
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 Vetter" <daniel.vetter@intel.com>, Andrew Morton <akpm@linux-foundation.org>, 
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 <dan.j.williams@intel.com>, Linux ARM <linux-arm-kernel@lists.infradead.org>, 
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References: <CAKMK7uEw701AWXNJbRNM8Z+FkyUB5FbWegmSzyWPy9cG4W7OLA@mail.gmail.com>
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 <20201105124950.GZ36674@ziepe.ca>
From: John Hubbard <jhubbard@nvidia.com>
Message-ID: <7ae3486d-095e-cf4e-6b0f-339d99709996@nvidia.com>
Date: Thu, 5 Nov 2020 20:08:10 -0800
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On 11/5/20 4:49 AM, Jason Gunthorpe wrote:
> On Thu, Nov 05, 2020 at 10:25:24AM +0100, Daniel Vetter wrote:
>>> /*
>>>   * If we can't determine whether or not a pte is special, then fail immediately
>>>   * for ptes. Note, we can still pin HugeTLB and THP as these are guaranteed not
>>>   * to be special.
>>>   *
>>>   * For a futex to be placed on a THP tail page, get_futex_key requires a
>>>   * get_user_pages_fast_only implementation that can pin pages. Thus it's still
>>>   * useful to have gup_huge_pmd even if we can't operate on ptes.
>>>   */
>>
>> We support hugepage faults in gpu drivers since recently, and I'm not
>> seeing a pud_mkhugespecial anywhere. So not sure this works, but probably
>> just me missing something again.
> 
> It means ioremap can't create an IO page PUD, it has to be broken up.
> 
> Does ioremap even create anything larger than PTEs?
> 

 From my reading, yes. See ioremap_try_huge_pmd().

thanks,
-- 
John Hubbard
NVIDIA

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From: John Hubbard <jhubbard@nvidia.com>
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On 11/5/20 4:49 AM, Jason Gunthorpe wrote:
> On Thu, Nov 05, 2020 at 10:25:24AM +0100, Daniel Vetter wrote:
>>> /*
>>>   * If we can't determine whether or not a pte is special, then fail immediately
>>>   * for ptes. Note, we can still pin HugeTLB and THP as these are guaranteed not
>>>   * to be special.
>>>   *
>>>   * For a futex to be placed on a THP tail page, get_futex_key requires a
>>>   * get_user_pages_fast_only implementation that can pin pages. Thus it's still
>>>   * useful to have gup_huge_pmd even if we can't operate on ptes.
>>>   */
>>
>> We support hugepage faults in gpu drivers since recently, and I'm not
>> seeing a pud_mkhugespecial anywhere. So not sure this works, but probably
>> just me missing something again.
> 
> It means ioremap can't create an IO page PUD, it has to be broken up.
> 
> Does ioremap even create anything larger than PTEs?
> 

 From my reading, yes. See ioremap_try_huge_pmd().

thanks,
-- 
John Hubbard
NVIDIA
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dri-devel@lists.freedesktop.org
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