linux-kernel - Re: [PATCH v4 RESEND 0/2] Align mmap address for DAX pmd mappings

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Date:   Mon, 29 Aug 2016 23:48:42 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Toshi Kani <toshi.kani@....com>
Cc:     akpm@...ux-foundation.org, dan.j.williams@...el.com,
        mawilcox@...rosoft.com, ross.zwisler@...ux.intel.com,
        kirill.shutemov@...ux.intel.com, david@...morbit.com, jack@...e.cz,
        tytso@....edu, adilger.kernel@...ger.ca, mike.kravetz@...cle.com,
        linux-nvdimm@...ts.01.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org, hughd@...gle.com
Subject: Re: [PATCH v4 RESEND 0/2] Align mmap address for DAX pmd mappings

On Mon, Aug 29, 2016 at 01:11:19PM -0600, Toshi Kani wrote:
> When CONFIG_FS_DAX_PMD is set, DAX supports mmap() using pmd page
> size.  This feature relies on both mmap virtual address and FS
> block (i.e. physical address) to be aligned by the pmd page size.
> Users can use mkfs options to specify FS to align block allocations.
> However, aligning mmap address requires code changes to existing
> applications for providing a pmd-aligned address to mmap().
> 
> For instance, fio with "ioengine=mmap" performs I/Os with mmap() [1].
> It calls mmap() with a NULL address, which needs to be changed to
> provide a pmd-aligned address for testing with DAX pmd mappings.
> Changing all applications that call mmap() with NULL is undesirable.
> 
> This patch-set extends filesystems to align an mmap address for
> a DAX file so that unmodified applications can use DAX pmd mappings.

+Hugh

Can we get it used for shmem/tmpfs too?
I don't think we should duplicate essentially the same functionality in
multiple places.

-- 
 Kirill A. Shutemov