On Fri, Feb 26, 2021 at 08:11:30PM +0100, David Sterba wrote:
> On Fri, Feb 26, 2021 at 06:34:36PM +0900, Naohiro Aota wrote:
> > This commit moves the location of superblock logging zones basing on the
> > static address instead of the static zone number.
> >
> > The following zones are reserved as the circular buffer on zoned btrfs.
> > - The primary superblock: zone at LBA 0 and the next zone
> > - The first copy: zone at LBA 16G and the next zone
> > - The second copy: zone at LBA 256G and the next zone
>
> This contains all the important information but somehow feels too short
> given how many mails we've exchanged and all the reasoning why we do
> that
Yep, sure. I'll expand the description and repost.
> >
> > We disallow zone size larger than 8GB not to overlap the superblock log
> > zones.
> >
> > Since the superblock zones overlap, we disallow zone size larger than 8GB.
>
> or why we chose 8G to be the reasonable upper limit for the zone size.
>
> > Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
> > ---
> > fs/btrfs/zoned.c | 21 +++++++++++++++------
> > 1 file changed, 15 insertions(+), 6 deletions(-)
> >
> > diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
> > index 9a5cf153da89..40cb99854844 100644
> > --- a/fs/btrfs/zoned.c
> > +++ b/fs/btrfs/zoned.c
> > @@ -112,10 +112,9 @@ static int sb_write_pointer(struct block_device *bdev, struct blk_zone *zones,
> >
> > /*
> > * The following zones are reserved as the circular buffer on ZONED btrfs.
> > - * - The primary superblock: zones 0 and 1
> > - * - The first copy: zones 16 and 17
> > - * - The second copy: zones 1024 or zone at 256GB which is minimum, and
> > - * the following one
> > + * - The primary superblock: zone at LBA 0 and the next zone
> > + * - The first copy: zone at LBA 16G and the next zone
> > + * - The second copy: zone at LBA 256G and the next zone
> > */
> > static inline u32 sb_zone_number(int shift, int mirror)
> > {
> > @@ -123,8 +122,8 @@ static inline u32 sb_zone_number(int shift, int mirror)
> >
> > switch (mirror) {
> > case 0: return 0;
> > - case 1: return 16;
> > - case 2: return min_t(u64, btrfs_sb_offset(mirror) >> shift, 1024);
> > + case 1: return 1 << (const_ilog2(SZ_16G) - shift);
> > + case 2: return 1 << (const_ilog2(SZ_1G) + 8 - shift);
>
> This ilog(SZ_1G) + 8 is confusing, it should have been 256G for clarity,
> as it's a constant it'll get expanded at compile time.
I'd like to use SZ_256G here, but linux/sizes.h does not define
it. I'll define one for us and use it in the next version.
> > }
> >
> > return 0;
> > @@ -300,6 +299,16 @@ int btrfs_get_dev_zone_info(struct btrfs_device *device)
> > zone_sectors = bdev_zone_sectors(bdev);
> > }
> >
> > + /* We don't support zone size > 8G that SB log zones overlap. */
> > + if (zone_sectors > (SZ_8G >> SECTOR_SHIFT)) {
> > + btrfs_err_in_rcu(fs_info,
> > + "zoned: %s: zone size %llu is too large",
> > + rcu_str_deref(device->name),
> > + (u64)zone_sectors << SECTOR_SHIFT);
> > + ret = -EINVAL;
> > + goto out;
> > + }
> > +
> > nr_sectors = bdev_nr_sectors(bdev);
> > /* Check if it's power of 2 (see is_power_of_2) */
> > ASSERT(zone_sectors != 0 && (zone_sectors & (zone_sectors - 1)) == 0);
> > --
> > 2.30.1
