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SubjectRe: [PATCH RFC 4/6] btrfs: Check if the filesystem is has mixed type of devices
On Wed, Feb 10, 2021 at 10:09:10AM +0000, Filipe Manana wrote:
> On Tue, Feb 9, 2021 at 9:32 PM Michal Rostecki <mrostecki@suse.de> wrote:
> >
> > From: Michal Rostecki <mrostecki@suse.com>
> >
> > Add the btrfs_check_mixed() function which checks if the filesystem has
> > the mixed type of devices (non-rotational and rotational). This
> > information is going to be used in roundrobin raid1 read policy.
> >
> > Signed-off-by: Michal Rostecki <mrostecki@suse.com>
> > ---
> > fs/btrfs/volumes.c | 44 ++++++++++++++++++++++++++++++++++++++++++--
> > fs/btrfs/volumes.h | 7 +++++++
> > 2 files changed, 49 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> > index 1ac364a2f105..1ad30a595722 100644
> > --- a/fs/btrfs/volumes.c
> > +++ b/fs/btrfs/volumes.c
> > @@ -617,6 +617,35 @@ static int btrfs_free_stale_devices(const char *path,
> > return ret;
> > }
> >
> > +/*
> > + * Checks if after adding the new device the filesystem is going to have mixed
> > + * types of devices (non-rotational and rotational).
> > + *
> > + * @fs_devices: list of devices
> > + * @new_device_rotating: if the new device is rotational
> > + *
> > + * Returns true if there are mixed types of devices, otherwise returns false.
> > + */
> > +static bool btrfs_check_mixed(struct btrfs_fs_devices *fs_devices,
> > + bool new_device_rotating)
> > +{
> > + struct btrfs_device *device, *prev_device;
> > +
> > + list_for_each_entry(device, &fs_devices->devices, dev_list) {
> > + if (prev_device == NULL &&
>
> Hum, prev_device is not initialized when we enter the first iteration
> of the loop.
>
> > + device->rotating != new_device_rotating)
> > + return true;
> > + if (prev_device != NULL &&
> > + (device->rotating != prev_device->rotating ||
>
> Here it's more dangerous, dereferencing an uninitialized pointer can
> result in a crash.
>
> With this fixed, it would be better to redo the benchmarks when using
> mixed device types.
>
> Thanks.
>

Thanks for pointing that out. Will fix and redo benchmarks for v2.

> > + device->rotating != new_device_rotating))
> > + return true;
> > +
> > + prev_device = device;
> > + }
> > +
> > + return false;
> > +}
> > +
> > /*
> > * This is only used on mount, and we are protected from competing things
> > * messing with our fs_devices by the uuid_mutex, thus we do not need the
> > @@ -629,6 +658,7 @@ static int btrfs_open_one_device(struct btrfs_fs_devices *fs_devices,
> > struct request_queue *q;
> > struct block_device *bdev;
> > struct btrfs_super_block *disk_super;
> > + bool rotating;
> > u64 devid;
> > int ret;
> >
> > @@ -669,8 +699,12 @@ static int btrfs_open_one_device(struct btrfs_fs_devices *fs_devices,
> > }
> >
> > q = bdev_get_queue(bdev);
> > - if (!blk_queue_nonrot(q))
> > + rotating = !blk_queue_nonrot(q);
> > + device->rotating = rotating;
> > + if (rotating)
> > fs_devices->rotating = true;
> > + if (!fs_devices->mixed)
> > + fs_devices->mixed = btrfs_check_mixed(fs_devices, rotating);
> >
> > device->bdev = bdev;
> > clear_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state);
> > @@ -2418,6 +2452,7 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info)
> > fs_devices->open_devices = 0;
> > fs_devices->missing_devices = 0;
> > fs_devices->rotating = false;
> > + fs_devices->mixed = false;
> > list_add(&seed_devices->seed_list, &fs_devices->seed_list);
> >
> > generate_random_uuid(fs_devices->fsid);
> > @@ -2522,6 +2557,7 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
> > int seeding_dev = 0;
> > int ret = 0;
> > bool locked = false;
> > + bool rotating;
> >
> > if (sb_rdonly(sb) && !fs_devices->seeding)
> > return -EROFS;
> > @@ -2621,8 +2657,12 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
> >
> > atomic64_add(device->total_bytes, &fs_info->free_chunk_space);
> >
> > - if (!blk_queue_nonrot(q))
> > + rotating = !blk_queue_nonrot(q);
> > + device->rotating = rotating;
> > + if (rotating)
> > fs_devices->rotating = true;
> > + if (!fs_devices->mixed)
> > + fs_devices->mixed = btrfs_check_mixed(fs_devices, rotating);
> >
> > orig_super_total_bytes = btrfs_super_total_bytes(fs_info->super_copy);
> > btrfs_set_super_total_bytes(fs_info->super_copy,
> > diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
> > index 6e544317a377..594f1207281c 100644
> > --- a/fs/btrfs/volumes.h
> > +++ b/fs/btrfs/volumes.h
> > @@ -147,6 +147,9 @@ struct btrfs_device {
> > /* I/O stats for raid1 mirror selection */
> > struct percpu_counter inflight;
> > atomic_t last_offset;
> > +
> > + /* If the device is rotational */
> > + bool rotating;
> > };
> >
> > /*
> > @@ -274,6 +277,10 @@ struct btrfs_fs_devices {
> > * nonrot flag set
> > */
> > bool rotating;
> > + /* Set when we find or add both nonrot and rot disks in the
> > + * filesystem
> > + */
> > + bool mixed;
> >
> > struct btrfs_fs_info *fs_info;
> > /* sysfs kobjects */
> > --
> > 2.30.0
> >
>
>
> --
> Filipe David Manana,
>
> “Whether you think you can, or you think you can't — you're right.”

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