mm: always enable thp for dax mappings (baabda26) · Commits · 戴 / test

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:

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

Ross 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:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

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);

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