On Tue 13-06-17 16:08:31, Dan Williams wrote: > 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. > > Cc: Jan Kara <[email protected]> > Cc: Christoph Hellwig <[email protected]> > Cc: Andrew Morton <[email protected]> > Cc: "Kirill A. Shutemov" <[email protected]> > Reviewed-by: Ross Zwisler <[email protected]> > Signed-off-by: Dan Williams <[email protected]>
OK, makes sense. I can imagine some people would like to tune whether DAX uses huge pages or not but that would make sense as a separate knob (possibly on per-fs basis) and let's wait for real requests for this functionality. So: Reviewed-by: Jan Kara <[email protected]> Honza > --- > include/linux/dax.h | 5 ----- > include/linux/fs.h | 6 ++++++ > include/linux/huge_mm.h | 5 +++++ > 3 files changed, 11 insertions(+), 5 deletions(-) > > diff --git a/include/linux/dax.h b/include/linux/dax.h > index 1f6b6072af64..cbaf3d53d66b 100644 > --- a/include/linux/dax.h > +++ b/include/linux/dax.h > @@ -151,11 +151,6 @@ 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); > diff --git a/include/linux/fs.h b/include/linux/fs.h > index 803e5a9b2654..5916ab3a12d5 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -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/fiemap.h> > @@ -3042,6 +3043,11 @@ 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; > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index c8119e856eb1..5a86f615f3cb 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -1,6 +1,8 @@ > #ifndef _LINUX_HUGE_MM_H > #define _LINUX_HUGE_MM_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, > @@ -95,6 +97,9 @@ 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); > -- Jan Kara <[email protected]> SUSE Labs, CR _______________________________________________ Linux-nvdimm mailing list [email protected] https://lists.01.org/mailman/listinfo/linux-nvdimm
