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[195.135.220.15]) by mx.google.com with ESMTPS id j133si1027045wmg.152.2017.06.14.03.05.47 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 14 Jun 2017 03:05:47 -0700 (PDT) Date: Wed, 14 Jun 2017 12:05:46 +0200 From: Jan Kara Subject: Re: [PATCH v2 2/2] mm: always enable thp for dax mappings Message-ID: <20170614100546.GC20247@quack2.suse.cz> References: <149739530052.20686.9000645746376519779.stgit@dwillia2-desk3.amr.corp.intel.com> <149739531127.20686.15813586620597484283.stgit@dwillia2-desk3.amr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <149739531127.20686.15813586620597484283.stgit@dwillia2-desk3.amr.corp.intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: Dan Williams Cc: akpm@linux-foundation.org, Jan Kara , linux-nvdimm@lists.01.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Ross Zwisler , hch@lst.de, "Kirill A. Shutemov" 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 > Cc: Christoph Hellwig > Cc: Andrew Morton > Cc: "Kirill A. Shutemov" > Reviewed-by: Ross Zwisler > Signed-off-by: Dan Williams 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 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 > #include > #include > +#include > #include > #include > #include > @@ -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 /* 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 SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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