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Message-ID: <20210127121635.GA29301@wotan.suse.de>
Date: Wed, 27 Jan 2021 12:16:35 +0000
From: Michal Rostecki <mrostecki@...e.de>
To: Filipe Manana <fdmanana@...il.com>
Cc: Michal Rostecki <mrostecki@...e.com>, Chris Mason <clm@...com>,
Josef Bacik <josef@...icpanda.com>,
David Sterba <dsterba@...e.com>,
Nikolay Borisov <nborisov@...e.com>,
linux-btrfs <linux-btrfs@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] btrfs: Avoid calling btrfs_get_chunk_map() twice
On Wed, Jan 27, 2021 at 11:20:55AM +0000, Filipe Manana wrote:
> On Wed, Jan 27, 2021 at 9:59 AM Michal Rostecki <mrostecki@...e.de> wrote:
> >
> > From: Michal Rostecki <mrostecki@...e.com>
> >
> > Before this change, the btrfs_get_io_geometry() function was calling
> > btrfs_get_chunk_map() to get the extent mapping, necessary for
> > calculating the I/O geometry. It was using that extent mapping only
> > internally and freeing the pointer after its execution.
> >
> > That resulted in calling btrfs_get_chunk_map() de facto twice by the
> > __btrfs_map_block() function. It was calling btrfs_get_io_geometry()
> > first and then calling btrfs_get_chunk_map() directly to get the extent
> > mapping, used by the rest of the function.
> >
> > This change fixes that by passing the extent mapping to the
> > btrfs_get_io_geometry() function as an argument.
> >
> > Fixes: 89b798ad1b42 ("btrfs: Use btrfs_get_io_geometry appropriately")
>
> Generally we only use the Fixes tag for bug fixes or serious
> performance regressions.
> Have you seen here a serious performance regression?
>
No, I didn't see any big difference in terms of performance (at least in
seq reads). I will remove the tag in v2.
> > Signed-off-by: Michal Rostecki <mrostecki@...e.com>
> > ---
> > fs/btrfs/inode.c | 37 ++++++++++++++++++++++++++++---------
> > fs/btrfs/volumes.c | 39 ++++++++++++++++-----------------------
> > fs/btrfs/volumes.h | 5 +++--
> > 3 files changed, 47 insertions(+), 34 deletions(-)
> >
> > diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> > index 0dbe1aaa0b71..a4ce8501ed4d 100644
> > --- a/fs/btrfs/inode.c
> > +++ b/fs/btrfs/inode.c
> > @@ -2183,9 +2183,10 @@ int btrfs_bio_fits_in_stripe(struct page *page, size_t size, struct bio *bio,
> > struct inode *inode = page->mapping->host;
> > struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> > u64 logical = bio->bi_iter.bi_sector << 9;
> > + struct extent_map *em;
> > u64 length = 0;
> > u64 map_length;
> > - int ret;
> > + int ret = 0;
> > struct btrfs_io_geometry geom;
> >
> > if (bio_flags & EXTENT_BIO_COMPRESSED)
> > @@ -2193,14 +2194,21 @@ int btrfs_bio_fits_in_stripe(struct page *page, size_t size, struct bio *bio,
> >
> > length = bio->bi_iter.bi_size;
> > map_length = length;
> > - ret = btrfs_get_io_geometry(fs_info, btrfs_op(bio), logical, map_length,
> > - &geom);
> > + em = btrfs_get_chunk_map(fs_info, logical, map_length);
> > + if (IS_ERR(em))
> > + return PTR_ERR(em);
> > + ret = btrfs_get_io_geometry(fs_info, em, btrfs_op(bio), logical,
> > + map_length, &geom);
> > if (ret < 0)
> > - return ret;
> > + goto out;
> >
> > - if (geom.len < length + size)
> > - return 1;
> > - return 0;
> > + if (geom.len < length + size) {
> > + ret = 1;
> > + goto out;
> > + }
> > +out:
> > + free_extent_map(em);
> > + return ret;
> > }
> >
> > /*
> > @@ -7941,10 +7949,12 @@ static blk_qc_t btrfs_submit_direct(struct inode *inode, struct iomap *iomap,
> > u64 submit_len;
> > int clone_offset = 0;
> > int clone_len;
> > + int logical;
> > int ret;
> > blk_status_t status;
> > struct btrfs_io_geometry geom;
> > struct btrfs_dio_data *dio_data = iomap->private;
> > + struct extent_map *em;
> >
> > dip = btrfs_create_dio_private(dio_bio, inode, file_offset);
> > if (!dip) {
> > @@ -7970,11 +7980,17 @@ static blk_qc_t btrfs_submit_direct(struct inode *inode, struct iomap *iomap,
> > }
> >
> > start_sector = dio_bio->bi_iter.bi_sector;
> > + logical = start_sector << 9;
> > submit_len = dio_bio->bi_iter.bi_size;
> >
> > do {
> > - ret = btrfs_get_io_geometry(fs_info, btrfs_op(dio_bio),
> > - start_sector << 9, submit_len,
> > + em = btrfs_get_chunk_map(fs_info, logical, submit_len);
> > + if (IS_ERR(em)) {
> > + status = errno_to_blk_status(ret);
> > + goto out_err;
>
> em must be set to NULL before going to "out_err", otherwise we get a
> crash due to an invalid memory access.
>
> Also, status should be set to "errno_to_blk_status(PTR_ERR(em))". The
> value of ret at this point is undefined.
>
> Other than that, it looks good.
>
> Thanks.
>
Will fix in v2. Thanks!
> > + }
> > + ret = btrfs_get_io_geometry(fs_info, em, btrfs_op(dio_bio),
> > + logical, submit_len,
> > &geom);
> > if (ret) {
> > status = errno_to_blk_status(ret);
> > @@ -8030,12 +8046,15 @@ static blk_qc_t btrfs_submit_direct(struct inode *inode, struct iomap *iomap,
> > clone_offset += clone_len;
> > start_sector += clone_len >> 9;
> > file_offset += clone_len;
> > +
> > + free_extent_map(em);
> > } while (submit_len > 0);
> > return BLK_QC_T_NONE;
> >
> > out_err:
> > dip->dio_bio->bi_status = status;
> > btrfs_dio_private_put(dip);
> > + free_extent_map(em);
> > return BLK_QC_T_NONE;
> > }
> >
> > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> > index a8ec8539cd8d..4c753b17c0a2 100644
> > --- a/fs/btrfs/volumes.c
> > +++ b/fs/btrfs/volumes.c
> > @@ -5940,23 +5940,24 @@ static bool need_full_stripe(enum btrfs_map_op op)
> > }
> >
> > /*
> > - * btrfs_get_io_geometry - calculates the geomery of a particular (address, len)
> > + * btrfs_get_io_geometry - calculates the geometry of a particular (address, len)
> > * tuple. This information is used to calculate how big a
> > * particular bio can get before it straddles a stripe.
> > *
> > - * @fs_info - the filesystem
> > - * @logical - address that we want to figure out the geometry of
> > - * @len - the length of IO we are going to perform, starting at @logical
> > - * @op - type of operation - write or read
> > - * @io_geom - pointer used to return values
> > + * @fs_info: the filesystem
> > + * @em: mapping containing the logical extent
> > + * @op: type of operation - write or read
> > + * @logical: address that we want to figure out the geometry of
> > + * @len: the length of IO we are going to perform, starting at @logical
> > + * @io_geom: pointer used to return values
> > *
> > * Returns < 0 in case a chunk for the given logical address cannot be found,
> > * usually shouldn't happen unless @logical is corrupted, 0 otherwise.
> > */
> > -int btrfs_get_io_geometry(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
> > - u64 logical, u64 len, struct btrfs_io_geometry *io_geom)
> > +int btrfs_get_io_geometry(struct btrfs_fs_info *fs_info, struct extent_map *em,
> > + enum btrfs_map_op op, u64 logical, u64 len,
> > + struct btrfs_io_geometry *io_geom)
> > {
> > - struct extent_map *em;
> > struct map_lookup *map;
> > u64 offset;
> > u64 stripe_offset;
> > @@ -5964,14 +5965,9 @@ int btrfs_get_io_geometry(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
> > u64 stripe_len;
> > u64 raid56_full_stripe_start = (u64)-1;
> > int data_stripes;
> > - int ret = 0;
> >
> > ASSERT(op != BTRFS_MAP_DISCARD);
> >
> > - em = btrfs_get_chunk_map(fs_info, logical, len);
> > - if (IS_ERR(em))
> > - return PTR_ERR(em);
> > -
> > map = em->map_lookup;
> > /* Offset of this logical address in the chunk */
> > offset = logical - em->start;
> > @@ -5985,8 +5981,7 @@ int btrfs_get_io_geometry(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
> > btrfs_crit(fs_info,
> > "stripe math has gone wrong, stripe_offset=%llu offset=%llu start=%llu logical=%llu stripe_len=%llu",
> > stripe_offset, offset, em->start, logical, stripe_len);
> > - ret = -EINVAL;
> > - goto out;
> > + return -EINVAL;
> > }
> >
> > /* stripe_offset is the offset of this block in its stripe */
> > @@ -6033,10 +6028,7 @@ int btrfs_get_io_geometry(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
> > io_geom->stripe_offset = stripe_offset;
> > io_geom->raid56_stripe_offset = raid56_full_stripe_start;
> >
> > -out:
> > - /* once for us */
> > - free_extent_map(em);
> > - return ret;
> > + return 0;
> > }
> >
> > static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
> > @@ -6069,12 +6061,13 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
> > ASSERT(bbio_ret);
> > ASSERT(op != BTRFS_MAP_DISCARD);
> >
> > - ret = btrfs_get_io_geometry(fs_info, op, logical, *length, &geom);
> > + em = btrfs_get_chunk_map(fs_info, logical, *length);
> > + ASSERT(!IS_ERR(em));
> > +
> > + ret = btrfs_get_io_geometry(fs_info, em, op, logical, *length, &geom);
> > if (ret < 0)
> > return ret;
> >
> > - em = btrfs_get_chunk_map(fs_info, logical, *length);
> > - ASSERT(!IS_ERR(em));
> > map = em->map_lookup;
> >
> > *length = geom.len;
> > diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
> > index c43663d9c22e..04e2b26823c2 100644
> > --- a/fs/btrfs/volumes.h
> > +++ b/fs/btrfs/volumes.h
> > @@ -440,8 +440,9 @@ int btrfs_map_block(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
> > int btrfs_map_sblock(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
> > u64 logical, u64 *length,
> > struct btrfs_bio **bbio_ret);
> > -int btrfs_get_io_geometry(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
> > - u64 logical, u64 len, struct btrfs_io_geometry *io_geom);
> > +int btrfs_get_io_geometry(struct btrfs_fs_info *fs_info, struct extent_map *map,
> > + enum btrfs_map_op op, u64 logical, u64 len,
> > + struct btrfs_io_geometry *io_geom);
> > int btrfs_read_sys_array(struct btrfs_fs_info *fs_info);
> > int btrfs_read_chunk_tree(struct btrfs_fs_info *fs_info);
> > int btrfs_alloc_chunk(struct btrfs_trans_handle *trans, u64 type);
> > --
> > 2.30.0
> >
>
>
> --
> Filipe David Manana,
>
> “Whether you think you can, or you think you can't — you're right.”
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