Re: [PATCH v3 0/2] Align mmap address for DAX pmd mappings

[Mike Kravetz <mike.kravetz@oracle.com>]

On 04/21/2016 12:06 AM, Matthew Wilcox wrote:
> On Wed, Apr 20, 2016 at 11:10:25PM -0400, Toshi Kani wrote:
>> How about moving the function (as is) to mm/huge_memory.c, rename it to
>> get_hugepage_unmapped_area(), which is defined to NULL in huge_mm.h
>> when TRANSPARENT_HUGEPAGE is unset?
> 
> Great idea.  Perhaps it should look something like this?
> 
> unsigned long thp_get_unmapped_area(struct file *filp, unsigned long addr,
>                 unsigned long len, unsigned long pgoff, unsigned long flags)
> {

Might want to keep the future possibility of PUD_SIZE THP in mind?
-- 
Mike Kravetz

>         loff_t off, off_end, off_pmd;
>         unsigned long len_pmd, addr_pmd;
> 
>         if (addr)
>                 goto out;
>         if (IS_DAX(filp->f_mapping->host) && !IS_ENABLED(CONFIG_FS_DAX_PMD))
>                 goto out;
>         /* Kirill, please fill in the right condition here for THP pagecache */
> 
>         off = (loff_t)pgoff << PAGE_SHIFT;
>         off_end = off + len;
>         off_pmd = round_up(off, PMD_SIZE);      /* pmd-aligned start offset */
> 
>         if ((off_end <= off_pmd) || ((off_end - off_pmd) < PMD_SIZE))
>                 goto out;
> 
>         len_pmd = len + PMD_SIZE;
>         if ((off + len_pmd) < off)
>                 goto out;
> 
>         addr_pmd = current->mm->get_unmapped_area(filp, NULL, len_pmd,
>                                                 pgoff, flags);
>         if (!IS_ERR_VALUE(addr_pmd)) {
>                 addr_pmd += (off - addr_pmd) & (PMD_SIZE - 1);
>                 return addr_pmd;
>         }
>  out:
>         return current->mm->get_unmapped_area(filp, addr, len, pgoff, flags);
> }
> 
>  - I deleted the check for filp == NULL.  It can't be NULL ... this is a
>    file_operation ;-)
>  - Why is len_pmd len + PMD_SIZE instead of round_up(len, PMD_SIZE)?
>  - I'm still in two minds about passing 'addr' to the first call to
>    get_unmapped_area() instead of NULL.
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