On Mon, 11 Jan 2021, David Laight wrote: > From: Al Viro <viro@xxxxxxxxxxxxxxxx> On Behalf Of Al Viro > > Sent: 10 January 2021 16:20 > > > > On Thu, Jan 07, 2021 at 08:15:41AM -0500, Mikulas Patocka wrote: > > > Hi > > > > > > I announce a new version of NVFS - a filesystem for persistent memory. > > > http://people.redhat.com/~mpatocka/nvfs/ > > Utilities, AFAICS > > > > > git://leontynka.twibright.com/nvfs.git > > Seems to hang on git pull at the moment... Do you have it anywhere else? > > > > > I found out that on NVFS, reading a file with the read method has 10% > > > better performance than the read_iter method. The benchmark just reads the > > > same 4k page over and over again - and the cost of creating and parsing > > > the kiocb and iov_iter structures is just that high. > > > > Apples and oranges... What happens if you take > > > > ssize_t read_iter_locked(struct file *file, struct iov_iter *to, loff_t *ppos) > > { > > struct inode *inode = file_inode(file); > > struct nvfs_memory_inode *nmi = i_to_nmi(inode); > > struct nvfs_superblock *nvs = inode->i_sb->s_fs_info; > > ssize_t total = 0; > > loff_t pos = *ppos; > > int r; > > int shift = nvs->log2_page_size; > > size_t i_size; > > > > i_size = inode->i_size; > > if (pos >= i_size) > > return 0; > > iov_iter_truncate(to, i_size - pos); > > > > while (iov_iter_count(to)) { > > void *blk, *ptr; > > size_t page_mask = (1UL << shift) - 1; > > unsigned page_offset = pos & page_mask; > > unsigned prealloc = (iov_iter_count(to) + page_mask) >> shift; > > unsigned size; > > > > blk = nvfs_bmap(nmi, pos >> shift, &prealloc, NULL, NULL, NULL); > > if (unlikely(IS_ERR(blk))) { > > r = PTR_ERR(blk); > > goto ret_r; > > } > > size = ((size_t)prealloc << shift) - page_offset; > > ptr = blk + page_offset; > > if (unlikely(!blk)) { > > size = min(size, (unsigned)PAGE_SIZE); > > ptr = empty_zero_page; > > } > > size = copy_to_iter(to, ptr, size); > > if (unlikely(!size)) { > > r = -EFAULT; > > goto ret_r; > > } > > > > pos += size; > > total += size; > > } while (iov_iter_count(to)); > > That isn't the best formed loop! > > David I removed the second "while" statement and fixed the arguments to copy_to_iter - other than that, Al's function works. Mikuklas
