On 2021/03/01 14:02, Naohiro Aota wrote:
> 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 <[email protected]>
>>> ---
>>> 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.
Or just use const_ilog2(256 * SZ_1G)... That is fairly easy to understand :)
I would even go further and add:
#define BTRFS_SB_FIRST_COPY_OFST (16ULL * SZ_1G)
#define BTRFS_SB_SECOND_COPY_OFST (256ULL * SZ_1G)
To be clear about what the values represent.
Then you can have:
+ case 1: return 1 << (const_ilog2(BTRFS_SB_FIRST_COPY_OFST) - shift);
+ case 2: return 1 << (const_ilog2(BTRFS_SB_SECOND_COPY_OFST) - shift);
>
>>> }
>>>
>>> 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
>
--
Damien Le Moal
Western Digital Research
