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

From: Matthew Wilcox
Date: Thu Apr 21 2016 - 03:06:00 EST

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

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)
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;
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.