From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Goldwyn Rodrigues <rgoldwyn@suse.de>
Cc: Filipe Manana <fdmanana@gmail.com>,
linux-btrfs <linux-btrfs@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH 4/7] btrfs: Use iomap_dio_rw() for direct I/O
Date: Tue, 19 Nov 2019 09:24:14 -0800 [thread overview]
Message-ID: <20191119172414.GT6235@magnolia> (raw)
In-Reply-To: <20191119170129.o4ml7p57soznxps7@fiona>
On Tue, Nov 19, 2019 at 11:01:29AM -0600, Goldwyn Rodrigues wrote:
> On 16:54 18/11, Filipe Manana wrote:
> > On Fri, Nov 15, 2019 at 4:19 PM Goldwyn Rodrigues <rgoldwyn@suse.de> wrote:
> > >
> > > From: Goldwyn Rodrigues <rgoldwyn@suse.com>
> > >
> > > This is the main patch to switch call from
> > > __blockdev_direct_IO() to iomap_dio_rw(). In this patch:
> > >
> > > Removed buffer_head references
> > > Removed inode_dio_begin() and inode_dio_end() functions since
> > > they are called in iomap_dio_rw().
> > > Renamed btrfs_get_blocks_direct() to direct_iomap_begin() and
> > > used it as iomap_begin()
> > > address_space.direct_IO now is a noop since direct_IO is called
> > > from __btrfs_write_direct().
> > >
> > > Removed flags parameter used for __blockdev_direct_IO(). iomap is
> > > capable of direct I/O reads from a hole, so we don't need to
> > > return -ENOENT.
> > >
> > > Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> > > ---
> > > fs/btrfs/ctree.h | 1 +
> > > fs/btrfs/file.c | 2 +-
> > > fs/btrfs/inode.c | 105 ++++++++++++++++++-------------------------------------
> > > 3 files changed, 36 insertions(+), 72 deletions(-)
> > >
> > > diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> > > index fe2b8765d9e6..cde8423673fc 100644
> > > --- a/fs/btrfs/ctree.h
> > > +++ b/fs/btrfs/ctree.h
> > > @@ -2903,6 +2903,7 @@ int btrfs_writepage_cow_fixup(struct page *page, u64 start, u64 end);
> > > void btrfs_writepage_endio_finish_ordered(struct page *page, u64 start,
> > > u64 end, int uptodate);
> > > extern const struct dentry_operations btrfs_dentry_operations;
> > > +ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter);
> > >
> > > /* ioctl.c */
> > > long btrfs_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
> > > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> > > index eede9dcbb4b6..d47da00fa61e 100644
> > > --- a/fs/btrfs/file.c
> > > +++ b/fs/btrfs/file.c
> > > @@ -1835,7 +1835,7 @@ static ssize_t __btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from)
> > > loff_t endbyte;
> > > int err;
> > >
> > > - written = generic_file_direct_write(iocb, from);
> > > + written = btrfs_direct_IO(iocb, from);
> > >
> > > if (written < 0 || !iov_iter_count(from))
> > > return written;
> > > diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> > > index c6dc4dd16cf7..e2e4dfb7a568 100644
> > > --- a/fs/btrfs/inode.c
> > > +++ b/fs/btrfs/inode.c
> > > @@ -8,6 +8,7 @@
> > > #include <linux/buffer_head.h>
> > > #include <linux/file.h>
> > > #include <linux/fs.h>
> > > +#include <linux/iomap.h>
> > > #include <linux/pagemap.h>
> > > #include <linux/highmem.h>
> > > #include <linux/time.h>
> > > @@ -7619,28 +7620,7 @@ static struct extent_map *create_io_em(struct inode *inode, u64 start, u64 len,
> > > }
> > >
> > >
> > > -static int btrfs_get_blocks_direct_read(struct extent_map *em,
> > > - struct buffer_head *bh_result,
> > > - struct inode *inode,
> > > - u64 start, u64 len)
> > > -{
> > > - if (em->block_start == EXTENT_MAP_HOLE ||
> > > - test_bit(EXTENT_FLAG_PREALLOC, &em->flags))
> > > - return -ENOENT;
> > > -
> > > - len = min(len, em->len - (start - em->start));
> > > -
> > > - bh_result->b_blocknr = (em->block_start + (start - em->start)) >>
> > > - inode->i_blkbits;
> > > - bh_result->b_size = len;
> > > - bh_result->b_bdev = em->bdev;
> > > - set_buffer_mapped(bh_result);
> > > -
> > > - return 0;
> > > -}
> > > -
> > > static int btrfs_get_blocks_direct_write(struct extent_map **map,
> > > - struct buffer_head *bh_result,
> > > struct inode *inode,
> > > struct btrfs_dio_data *dio_data,
> > > u64 start, u64 len)
> > > @@ -7702,7 +7682,6 @@ static int btrfs_get_blocks_direct_write(struct extent_map **map,
> > > }
> > >
> > > /* this will cow the extent */
> > > - len = bh_result->b_size;
> > > free_extent_map(em);
> > > *map = em = btrfs_new_extent_direct(inode, start, len);
> > > if (IS_ERR(em)) {
> > > @@ -7713,15 +7692,6 @@ static int btrfs_get_blocks_direct_write(struct extent_map **map,
> > > len = min(len, em->len - (start - em->start));
> > >
> > > skip_cow:
> > > - bh_result->b_blocknr = (em->block_start + (start - em->start)) >>
> > > - inode->i_blkbits;
> > > - bh_result->b_size = len;
> > > - bh_result->b_bdev = em->bdev;
> > > - set_buffer_mapped(bh_result);
> > > -
> > > - if (!test_bit(EXTENT_FLAG_PREALLOC, &em->flags))
> > > - set_buffer_new(bh_result);
> > > -
> > > /*
> > > * Need to update the i_size under the extent lock so buffered
> > > * readers will get the updated i_size when we unlock.
> > > @@ -7737,17 +7707,18 @@ static int btrfs_get_blocks_direct_write(struct extent_map **map,
> > > return ret;
> > > }
> > >
> > > -static int btrfs_get_blocks_direct(struct inode *inode, sector_t iblock,
> > > - struct buffer_head *bh_result, int create)
> > > +static int direct_iomap_begin(struct inode *inode, loff_t start,
> > > + loff_t length, unsigned flags, struct iomap *iomap,
> > > + struct iomap *srcmap)
> > > {
> > > struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> > > struct extent_map *em;
> > > struct extent_state *cached_state = NULL;
> > > struct btrfs_dio_data *dio_data = NULL;
> > > - u64 start = iblock << inode->i_blkbits;
> > > u64 lockstart, lockend;
> > > - u64 len = bh_result->b_size;
> > > + int create = flags & IOMAP_WRITE;
> > > int ret = 0;
> > > + u64 len = length;
> > >
> > > if (!create)
> > > len = min_t(u64, len, fs_info->sectorsize);
> > > @@ -7803,7 +7774,7 @@ static int btrfs_get_blocks_direct(struct inode *inode, sector_t iblock,
> > > }
> > >
> > > if (create) {
> > > - ret = btrfs_get_blocks_direct_write(&em, bh_result, inode,
> > > + ret = btrfs_get_blocks_direct_write(&em, inode,
> > > dio_data, start, len);
> > > if (ret < 0)
> > > goto unlock_err;
> > > @@ -7811,19 +7782,13 @@ static int btrfs_get_blocks_direct(struct inode *inode, sector_t iblock,
> > > unlock_extent_cached(&BTRFS_I(inode)->io_tree, lockstart,
> > > lockend, &cached_state);
> > > } else {
> > > - ret = btrfs_get_blocks_direct_read(em, bh_result, inode,
> > > - start, len);
> > > - /* Can be negative only if we read from a hole */
> > > - if (ret < 0) {
> > > - ret = 0;
> > > - free_extent_map(em);
> > > - goto unlock_err;
> > > - }
> > > +
> > > + len = min(len, em->len - (start - em->start));
> > > /*
> > > * We need to unlock only the end area that we aren't using.
> > > * The rest is going to be unlocked by the endio routine.
> > > */
> > > - lockstart = start + bh_result->b_size;
> > > + lockstart = start + len;
> > > if (lockstart < lockend) {
> > > unlock_extent_cached(&BTRFS_I(inode)->io_tree,
> > > lockstart, lockend, &cached_state);
> > > @@ -7832,6 +7797,18 @@ static int btrfs_get_blocks_direct(struct inode *inode, sector_t iblock,
> > > }
> > > }
> > >
> > > + if ((em->block_start == EXTENT_MAP_HOLE) ||
> > > + (test_bit(EXTENT_FLAG_PREALLOC, &em->flags) && !create)) {
> > > + iomap->addr = IOMAP_NULL_ADDR;
> > > + iomap->type = IOMAP_HOLE;
> > > + } else {
> > > + iomap->addr = em->block_start - (start - em->start);
> > > + iomap->type = IOMAP_MAPPED;
> > > + }
> > > + iomap->offset = start;
> > > + iomap->bdev = em->bdev;
> > > + iomap->length = min(len, em->len - (start - em->start));
> > > +
> > > free_extent_map(em);
> > >
> > > return 0;
> > > @@ -8199,9 +8176,8 @@ static void btrfs_endio_direct_read(struct bio *bio)
> > > kfree(dip);
> > >
> > > dio_bio->bi_status = err;
> > > - dio_end_io(dio_bio);
> > > + bio_endio(dio_bio);
> > > btrfs_io_bio_free_csum(io_bio);
> > > - bio_put(bio);
> > > }
> > >
> > > static void __endio_write_update_ordered(struct inode *inode,
> > > @@ -8263,8 +8239,7 @@ static void btrfs_endio_direct_write(struct bio *bio)
> > > kfree(dip);
> > >
> > > dio_bio->bi_status = bio->bi_status;
> > > - dio_end_io(dio_bio);
> > > - bio_put(bio);
> > > + bio_endio(dio_bio);
> > > }
> > >
> > > static blk_status_t btrfs_submit_bio_start_direct_io(void *private_data,
> > > @@ -8568,7 +8543,7 @@ static void btrfs_submit_direct(struct bio *dio_bio, struct inode *inode,
> > > /*
> > > * The end io callbacks free our dip, do the final put on bio
> > > * and all the cleanup and final put for dio_bio (through
> > > - * dio_end_io()).
> > > + * end_io()).
> > > */
> > > dip = NULL;
> > > bio = NULL;
> > > @@ -8587,7 +8562,7 @@ static void btrfs_submit_direct(struct bio *dio_bio, struct inode *inode,
> > > * Releases and cleans up our dio_bio, no need to bio_put()
> > > * nor bio_endio()/bio_io_error() against dio_bio.
> > > */
> > > - dio_end_io(dio_bio);
> > > + bio_endio(dio_bio);
> >
> > The comment above also needs to be updated. It explicitly mentions
> > there's no need to call bio_endio(), but now the code it's calling
> > that function.
> >
> > > }
> > > if (bio)
> > > bio_put(bio);
> > > @@ -8627,7 +8602,11 @@ static ssize_t check_direct_IO(struct btrfs_fs_info *fs_info,
> > > return retval;
> > > }
> > >
> > > -static ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
> > > +static const struct iomap_ops dio_iomap_ops = {
> > > + .iomap_begin = direct_iomap_begin,
> > > +};
> > > +
> > > +ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
> > > {
> > > struct file *file = iocb->ki_filp;
> > > struct inode *inode = file->f_mapping->host;
> > > @@ -8637,14 +8616,11 @@ static ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
> > > loff_t offset = iocb->ki_pos;
> > > size_t count = 0;
> > > int flags = 0;
> > > - bool wakeup = true;
> > > - bool relock = false;
> > > ssize_t ret;
> > >
> > > if (check_direct_IO(fs_info, iter, offset))
> > > return 0;
> > >
> > > - inode_dio_begin(inode);
> > >
> > > /*
> > > * The generic stuff only does filemap_write_and_wait_range, which
> > > @@ -8664,11 +8640,7 @@ static ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
> > > * the isize, but it is protected by i_mutex. So we can
> > > * not unlock the i_mutex at this case.
> > > */
> > > - if (offset + count <= inode->i_size) {
> > > - dio_data.overwrite = 1;
> > > - inode_unlock(inode);
> > > - relock = true;
> >
> > I'm not familiar with iomap, but a quick grep at iomap/*.c (5.4-rc7)
> > reveals no call to inode_unlock().
iomap doesn't handle locking at all -- it's the caller's responsibility
to set up the locking correctly before calling iomap_dio_rw.
> > So this change is throwing away the optimization done by commit [1],
> > which makes a lot of sense and when it landed I observed as well that
> > it made a great difference (as expected).
> > Correct me if I'm wrong, but that optimization is now gone isn't it?
> > So concurrent direct IO writes to a file, that don't expand the
> > inode's i_size and operate on non-overlapping ranges, will now be
> > completely serialized.
Yeah, I was thinking that too...
> Yes, I did not realize the consequences. Let me check the performance
> and if we can rope in this optimization with the existing iomap
> codebase. Thanks for pointing it out.
...though I see in the old code you'd drop the inode lock before calling
__blockdev_direct_IO, which (I hope) implies that it's safe to grab an
extent mapping and turn that into a struct bio without holding the inode
lock. If that's the case, there's no reason why you can't do the same
thing with iomap.
--D
> --
> Goldwyn
>
> >
> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=38851cc19adbfa1def2b47106d8050a80e0a3673
> >
> > Thanks
> >
> >
> > > - } else if (iocb->ki_flags & IOCB_NOWAIT) {
> > > + if (iocb->ki_flags & IOCB_NOWAIT) {
> > > ret = -EAGAIN;
> > > goto out;
> > > }
> > > @@ -8690,15 +8662,11 @@ static ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
> > > down_read(&BTRFS_I(inode)->dio_sem);
> > > } else if (test_bit(BTRFS_INODE_READDIO_NEED_LOCK,
> > > &BTRFS_I(inode)->runtime_flags)) {
> > > - inode_dio_end(inode);
> > > flags = DIO_LOCKING | DIO_SKIP_HOLES;
> > > - wakeup = false;
> > > }
> > >
> > > - ret = __blockdev_direct_IO(iocb, inode,
> > > - fs_info->fs_devices->latest_bdev,
> > > - iter, btrfs_get_blocks_direct, NULL,
> > > - btrfs_submit_direct, flags);
> > > + ret = iomap_dio_rw(iocb, iter, &dio_iomap_ops, NULL, is_sync_kiocb(iocb));
> > > +
> > > if (iov_iter_rw(iter) == WRITE) {
> > > up_read(&BTRFS_I(inode)->dio_sem);
> > > current->journal_info = NULL;
> > > @@ -8725,11 +8693,6 @@ static ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
> > > btrfs_delalloc_release_extents(BTRFS_I(inode), count);
> > > }
> > > out:
> > > - if (wakeup)
> > > - inode_dio_end(inode);
> > > - if (relock)
> > > - inode_lock(inode);
> > > -
> > > extent_changeset_free(data_reserved);
> > > return ret;
> > > }
> > > --
> > > 2.16.4
> > >
> >
> >
> > --
> > Filipe David Manana,
> >
> > “Whether you think you can, or you think you can't — you're right.”
>
> --
> Goldwyn
next prev parent reply other threads:[~2019-11-19 17:26 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-15 16:16 btrfs direct-io using iomap Goldwyn Rodrigues
2019-11-15 16:16 ` [PATCH 1/7] fs: Export generic_file_buffered_read() Goldwyn Rodrigues
2019-11-15 16:16 ` [PATCH 2/7] btrfs: basic direct I/O read operation Goldwyn Rodrigues
2019-11-15 16:45 ` Christoph Hellwig
2019-11-15 16:16 ` [PATCH 3/7] iomap: use a function pointer for dio submits Goldwyn Rodrigues
2019-11-15 16:47 ` Christoph Hellwig
2019-11-15 20:11 ` Goldwyn Rodrigues
2019-11-15 16:16 ` [PATCH 4/7] btrfs: Use iomap_dio_rw() for direct I/O Goldwyn Rodrigues
2019-11-15 17:06 ` Christoph Hellwig
2019-11-18 15:54 ` Goldwyn Rodrigues
2019-11-18 16:54 ` Filipe Manana
2019-11-19 17:01 ` Goldwyn Rodrigues
2019-11-19 17:24 ` Darrick J. Wong [this message]
2019-11-15 16:16 ` [PATCH 5/7] btrfs: Use iomap_dio_ops.submit_io() Goldwyn Rodrigues
2019-11-15 16:47 ` Christoph Hellwig
2019-11-15 16:16 ` [PATCH 6/7] btrfs: flush dirty pages on compressed I/O for dio Goldwyn Rodrigues
2019-11-15 16:50 ` Christoph Hellwig
2019-11-15 16:17 ` [PATCH 7/7] btrfs: Wait for extent bits to release page Goldwyn Rodrigues
2019-11-15 16:56 ` Christoph Hellwig
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