Re: [PATCH v4 RESEND 1/2] thp, dax: add thp_get_unmapped_area for pmd mappings

[Dan Williams]

On Mon, Aug 29, 2016 at 12:11 PM, Toshi Kani <toshi.kani@xxxxxxx> 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@xxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
> Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Dave Chinner <david@xxxxxxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Theodore Ts'o <tytso@xxxxxxx>
> Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx>
> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> ---

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

...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.