From: Dan Williams <dan.j.williams@intel.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Toshi Kani <toshi.kani@hpe.com>,
Andrew Morton <akpm@linux-foundation.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Matthew Wilcox <willy@linux.intel.com>,
Ross Zwisler <ross.zwisler@linux.intel.com>,
mauricio.porto@hpe.com, Linux MM <linux-mm@kvack.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@ml01.01.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: Fix mmap MAP_POPULATE for DAX pmd mapping
Date: Wed, 2 Dec 2015 14:03:46 -0800 [thread overview]
Message-ID: <CAPcyv4i0n=2+WMACVumvMHsXZ7xzBuzvO6WA9H06N_-S=s3ibQ@mail.gmail.com> (raw)
In-Reply-To: <565F69FE.601@intel.com>
On Wed, Dec 2, 2015 at 2:00 PM, Dave Hansen <dave.hansen@intel.com> wrote:
> On 12/02/2015 12:54 PM, Dan Williams wrote:
>> On Wed, Dec 2, 2015 at 1:37 PM, Toshi Kani <toshi.kani@hpe.com> wrote:
>>> > On Wed, 2015-12-02 at 11:57 -0800, Dan Williams wrote:
>> [..]
>>>> >> The whole point of __get_user_page_fast() is to avoid the overhead of
>>>> >> taking the mm semaphore to access the vma. _PAGE_SPECIAL simply tells
>>>> >> __get_user_pages_fast that it needs to fallback to the
>>>> >> __get_user_pages slow path.
>>> >
>>> > I see. Then, I think gup_huge_pmd() can simply return 0 when !pfn_valid(),
>>> > instead of VM_BUG_ON.
>> Is pfn_valid() a reliable check? It seems to be based on a max_pfn
>> per node... what happens when pmem is located below that point. I
>> haven't been able to convince myself that we won't get false
>> positives, but maybe I'm missing something.
>
> With sparsemem at least, it makes sure that you're looking at a valid
> _section_. See the pfn_valid() at ~include/linux/mmzone.h:1222.
At a minimum we would need to add "depends on SPARSEMEM" to "config FS_DAX_PMD".
next prev parent reply other threads:[~2015-12-02 22:03 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-23 20:04 [PATCH] mm: Fix mmap MAP_POPULATE for DAX pmd mapping Toshi Kani
2015-11-23 20:53 ` Dan Williams
2015-11-23 22:15 ` Toshi Kani
2015-11-30 22:08 ` Dan Williams
2015-12-02 2:19 ` Toshi Kani
2015-12-02 3:45 ` Dan Williams
2015-12-02 17:43 ` Toshi Kani
2015-12-02 17:01 ` Dan Williams
2015-12-02 18:06 ` Dan Williams
2015-12-02 19:26 ` Toshi Kani
2015-12-02 19:00 ` Dan Williams
2015-12-02 20:02 ` Toshi Kani
2015-12-02 20:12 ` Toshi Kani
2015-12-02 19:57 ` Dan Williams
2015-12-02 21:37 ` Toshi Kani
2015-12-02 20:54 ` Dan Williams
2015-12-02 21:55 ` Toshi Kani
2015-12-03 23:43 ` Dan Williams
2015-12-04 16:55 ` Toshi Kani
2015-12-02 22:00 ` Dave Hansen
2015-12-02 22:03 ` Dan Williams [this message]
2015-12-02 22:09 ` Dave Hansen
2015-12-03 0:21 ` Toshi Kani
2015-12-02 23:33 ` Dan Williams
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