From: David Laight <David.Laight@ACULAB.COM>
To: 'Al Viro' <viro@zeniv.linux.org.uk>,
Mikulas Patocka <mpatocka@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Dan Williams <dan.j.williams@intel.com>,
Vishal Verma <vishal.l.verma@intel.com>,
"Dave Jiang" <dave.jiang@intel.com>,
Ira Weiny <ira.weiny@intel.com>,
"Matthew Wilcox" <willy@infradead.org>, Jan Kara <jack@suse.cz>,
Steven Whitehouse <swhiteho@redhat.com>,
Eric Sandeen <esandeen@redhat.com>,
Dave Chinner <dchinner@redhat.com>, Theodore Ts'o <tytso@mit.edu>,
Wang Jianchao <jianchao.wan9@gmail.com>,
"Kani, Toshi" <toshi.kani@hpe.com>,
"Norton, Scott J" <scott.norton@hpe.com>,
"Tadakamadla, Rajesh" <rajesh.tadakamadla@hpe.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>
Subject: RE: [RFC v2] nvfs: a filesystem for persistent memory
Date: Mon, 11 Jan 2021 10:29:28 +0000 [thread overview]
Message-ID: <c26db2b0ea1a4891a7cbd0363de856d3@AcuMS.aculab.com> (raw)
In-Reply-To: <20210110162008.GV3579531@ZenIV.linux.org.uk>
From: Al Viro <viro@ftp.linux.org.uk> 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
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2021-01-11 10:31 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-07 13:15 [RFC v2] nvfs: a filesystem for persistent memory Mikulas Patocka
2021-01-07 15:11 ` Expense of read_iter Matthew Wilcox
2021-01-07 16:43 ` Mingkai Dong
2021-01-12 13:45 ` Zhongwei Cai
2021-01-12 14:06 ` David Laight
2021-01-13 16:44 ` Mikulas Patocka
2021-01-15 9:40 ` Zhongwei Cai
2021-01-20 4:47 ` Dave Chinner
2021-01-20 14:18 ` Jan Kara
2021-01-20 15:12 ` Mikulas Patocka
2021-01-20 15:44 ` David Laight
2021-01-21 15:47 ` Matthew Wilcox
2021-01-21 16:06 ` Mikulas Patocka
2021-01-21 16:30 ` Zhongwei Cai
2021-01-07 18:59 ` Mikulas Patocka
2021-01-10 6:13 ` Matthew Wilcox
2021-01-10 21:19 ` Mikulas Patocka
2021-01-11 0:18 ` Matthew Wilcox
2021-01-11 21:10 ` Mikulas Patocka
2021-01-11 10:11 ` David Laight
2021-01-10 16:20 ` [RFC v2] nvfs: a filesystem for persistent memory Al Viro
2021-01-10 16:51 ` Al Viro
2021-01-10 21:14 ` Mikulas Patocka
2021-01-10 23:40 ` Al Viro
2021-01-11 11:41 ` Mikulas Patocka
2021-01-11 10:29 ` David Laight [this message]
2021-01-11 11:44 ` Mikulas Patocka
2021-01-11 11:57 ` David Laight
2021-01-11 14:43 ` Al Viro
2021-01-11 14:54 ` David Laight
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