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Commit baabda26 authored by Dan Williams's avatar Dan Williams Committed by Linus Torvalds
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mm: always enable thp for dax mappings 

The madvise policy for transparent huge pages is meant to avoid unwanted
allocations of transparent huge pages.  It allows a policy of disabling
the extra memory pressure and effort to arrange for a huge page when it
is not needed.

DAX by definition never incurs this overhead since it is statically
allocated.  The policy choice makes even less sense for device-dax which
tries to guarantee a given tlb-fault size.  Specifically, the following
setting:

	echo never > /sys/kernel/mm/transparent_hugepage/enabled

...violates that guarantee and silently disables all device-dax
instances with a 2M or 1G alignment.  So, let's avoid that non-obvious
side effect by force enabling thp for dax mappings in all cases.

It is worth noting that the reason this uses vma_is_dax(), and the
resulting header include changes, is that previous attempts to add a
VM_DAX flag were NAKd.

Link: http://lkml.kernel.org/r/149739531127.20686.15813586620597484283.stgit@dwillia2-desk3.amr.corp.intel.com


Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
Reviewed-by: default avatarRoss Zwisler <ross.zwisler@linux.intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@lst.de>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 16981d76

include/linux/dax.h

+0 −5
Original line number Diff line number Diff line
@@ -154,11 +154,6 @@ static inline unsigned int dax_radix_order(void *entry) 
#endif

int dax_pfn_mkwrite(struct vm_fault *vmf);



static inline bool vma_is_dax(struct vm_area_struct *vma)

{

	return vma->vm_file && IS_DAX(vma->vm_file->f_mapping->host);

}



static inline bool dax_mapping(struct address_space *mapping)

{

	return mapping->host && IS_DAX(mapping->host);

include/linux/fs.h

+6 −0
Original line number Diff line number Diff line
@@ -18,6 +18,7 @@ 
#include <linux/bug.h>

#include <linux/mutex.h>

#include <linux/rwsem.h>

#include <linux/mm_types.h>

#include <linux/capability.h>

#include <linux/semaphore.h>

#include <linux/fcntl.h>
@@ -3127,6 +3128,11 @@ static inline bool io_is_direct(struct file *filp) 
	return (filp->f_flags & O_DIRECT) || IS_DAX(filp->f_mapping->host);

}



static inline bool vma_is_dax(struct vm_area_struct *vma)

{

	return vma->vm_file && IS_DAX(vma->vm_file->f_mapping->host);

}



static inline int iocb_flags(struct file *file)

{

	int res = 0;

include/linux/huge_mm.h

+5 −0
Original line number Diff line number Diff line
@@ -3,6 +3,8 @@ 


#include <linux/sched/coredump.h>



#include <linux/fs.h> /* only for vma_is_dax() */



extern int do_huge_pmd_anonymous_page(struct vm_fault *vmf);

extern int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,

			 pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
@@ -103,6 +105,9 @@ static inline bool transparent_hugepage_enabled(struct vm_area_struct *vma) 
	if (transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_FLAG))

		return true;



	if (vma_is_dax(vma))

		return true;



	if (transparent_hugepage_flags &

				(1 << TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG))

		return !!(vma->vm_flags & VM_HUGEPAGE);