DAX provides direct access to NVDIMM and bypasses the page caches. Newly introduced map_pages() callback reduces page faults by adding mappings around a faulted page, which is not supported for DAX.
This patch implements map_pages() callback for DAX. It reduces a number of page faults and increases read performance of DAX as shown below. The values in parenthesis are relative to the base DAX results. iozone results of mmap read/re-read tests [KB/sec] 64KB: read: 3,560,777 (x1.6) re-read: 9,086,412 (x1.8) pfault: 121 (-20%) 128MB: read: 4,374,906 (x1.7) re-read: 6,137,189 (x2.4) pfault: 8,312 (-87%) Signed-off-by: Toshi Kani <toshi.k...@hp.com> ---- Applies on top of DAX patchset [1] and fault-around patchset [2]. [1] https://lkml.org/lkml/2014/2/25/460 [2] https://lkml.org/lkml/2014/2/27/546 --- fs/dax.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++++ fs/ext4/file.c | 6 +++++ include/linux/fs.h | 5 ++++ 3 files changed, 79 insertions(+) diff --git a/fs/dax.c b/fs/dax.c index c8dfab0..bc54705 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -476,3 +476,71 @@ int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length, return 0; } EXPORT_SYMBOL_GPL(dax_zero_page_range); + +static void dax_set_pte(struct vm_area_struct *vma, unsigned long addr, + unsigned long pfn, pte_t *pte) +{ + pte_t entry; + + if (addr < vma->vm_start || addr >= vma->vm_end) + return; + + if (!pte_none(*pte)) + return; + + entry = pte_mkspecial(pfn_pte(pfn, vma->vm_page_prot)); + set_pte_at(vma->vm_mm, addr, pte, entry); + update_mmu_cache(vma, addr, pte); +} + +void dax_map_pages(struct vm_area_struct *vma, struct vm_fault *vmf, + get_block_t get_block) +{ + struct file *file = vma->vm_file; + struct inode *inode = file_inode(file); + struct buffer_head bh; + struct address_space *mapping = file->f_mapping; + unsigned long vaddr = (unsigned long)vmf->virtual_address; + pgoff_t pgoff = vmf->pgoff; + sector_t block; + pgoff_t size; + unsigned long pfn; + pte_t *pte = vmf->pte; + int error; + + while (pgoff < vmf->max_pgoff) { + size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT; + if (pgoff >= size) + return; + + memset(&bh, 0, sizeof(bh)); + block = (sector_t)pgoff << (PAGE_SHIFT - inode->i_blkbits); + bh.b_size = PAGE_SIZE; + error = get_block(inode, block, &bh, 0); + if (error || bh.b_size < PAGE_SIZE) + goto next; + + if (!buffer_mapped(&bh) || buffer_unwritten(&bh) || + buffer_new(&bh)) + goto next; + + /* Recheck i_size under i_mmap_mutex */ + mutex_lock(&mapping->i_mmap_mutex); + size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT; + if (unlikely(pgoff >= size)) { + mutex_unlock(&mapping->i_mmap_mutex); + return; + } + + error = dax_get_pfn(inode, &bh, &pfn); + if (error > 0) + dax_set_pte(vma, vaddr, pfn, pte); + + mutex_unlock(&mapping->i_mmap_mutex); +next: + vaddr += PAGE_SIZE; + pgoff++; + pte++; + } +} +EXPORT_SYMBOL_GPL(dax_map_pages); diff --git a/fs/ext4/file.c b/fs/ext4/file.c index eb19383..15965ea 100644 --- a/fs/ext4/file.c +++ b/fs/ext4/file.c @@ -205,6 +205,11 @@ static int ext4_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf) /* Is this the right get_block? */ } +static void ext4_dax_map_pages(struct vm_area_struct *vma, struct vm_fault *vmf) +{ + return dax_map_pages(vma, vmf, ext4_get_block); +} + static int ext4_dax_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf) { return dax_mkwrite(vma, vmf, ext4_get_block); @@ -212,6 +217,7 @@ static int ext4_dax_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf) static const struct vm_operations_struct ext4_dax_vm_ops = { .fault = ext4_dax_fault, + .map_pages = ext4_dax_map_pages, .page_mkwrite = ext4_dax_mkwrite, .remap_pages = generic_file_remap_pages, }; diff --git a/include/linux/fs.h b/include/linux/fs.h index d0381ab..3bd1042 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2527,6 +2527,7 @@ ssize_t dax_do_io(int rw, struct kiocb *, struct inode *, const struct iovec *, loff_t, unsigned segs, get_block_t, dio_iodone_t, int flags); int dax_fault(struct vm_area_struct *, struct vm_fault *, get_block_t); int dax_mkwrite(struct vm_area_struct *, struct vm_fault *, get_block_t); +void dax_map_pages(struct vm_area_struct *, struct vm_fault *, get_block_t); #else static inline int dax_clear_blocks(struct inode *i, sector_t blk, long sz) { @@ -2545,6 +2546,10 @@ static inline ssize_t dax_do_io(int rw, struct kiocb *iocb, struct inode *inode, { return -ENOTTY; } +static inline void dax_map_pages(struct vm_area_struct *vma, + struct vm_fault *vmf, get_block_t get_block) +{ +} #endif /* Can't be a function because PAGE_CACHE_SIZE is defined in pagemap.h */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
