linux-kernel - Re: [PATCH v4 RESEND 1/2] thp, dax: add thp_get_unmapped

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Date:   Mon, 29 Aug 2016 12:34:21 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Toshi Kani <toshi.kani@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        david <david@...morbit.com>, Jan Kara <jack@...e.cz>,
        "Theodore Ts'o" <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        mike.kravetz@...cle.com,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 RESEND 1/2] thp, dax: add thp_get_unmapped_area for pmd mappings

On Mon, Aug 29, 2016 at 12:11 PM, Toshi Kani <toshi.kani@....com> 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.
>
> Add thp_get_unmapped_area(), which can be called by filesystem's
> get_unmapped_area to align an mmap address by the pmd size for
> a DAX file.  It calls the default handler, mm->get_unmapped_area(),
> to find a range and then aligns it for a DAX file.
>
> The patch is based on Matthew Wilcox's change that allows adding
> support of the pud page size easily.
>
> [1]: https://github.com/axboe/fio/blob/master/engines/mmap.c
> Signed-off-by: Toshi Kani <toshi.kani@....com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Matthew Wilcox <mawilcox@...rosoft.com>
> Cc: Ross Zwisler <ross.zwisler@...ux.intel.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Dave Chinner <david@...morbit.com>
> Cc: Jan Kara <jack@...e.cz>
> Cc: Theodore Ts'o <tytso@....edu>
> Cc: Andreas Dilger <adilger.kernel@...ger.ca>
> Cc: Mike Kravetz <mike.kravetz@...cle.com>
> ---

Reviewed-by: Dan Williams <dan.j.williams@...el.com>

...with one minor nit:


>  include/linux/huge_mm.h |    7 +++++++
>  mm/huge_memory.c        |   43 +++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 50 insertions(+)
>
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 6f14de4..4fca526 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -87,6 +87,10 @@ extern bool is_vma_temporary_stack(struct vm_area_struct *vma);
>
>  extern unsigned long transparent_hugepage_flags;
>
> +extern unsigned long thp_get_unmapped_area(struct file *filp,
> +               unsigned long addr, unsigned long len, unsigned long pgoff,
> +               unsigned long flags);
> +
>  extern void prep_transhuge_page(struct page *page);
>  extern void free_transhuge_page(struct page *page);
>
> @@ -169,6 +173,9 @@ void put_huge_zero_page(void);
>  static inline void prep_transhuge_page(struct page *page) {}
>
>  #define transparent_hugepage_flags 0UL
> +
> +#define thp_get_unmapped_area  NULL

Lets make this:

static inline unsigned long thp_get_unmapped_area(struct file *filp,
               unsigned long addr, unsigned long len, unsigned long pgoff,
               unsigned long flags)
{
    return 0;
}

...to get some type checking in the CONFIG_TRANSPARENT_HUGEPAGE=n case.