Re: [PATCH V7 11/17] xfs: Introduce macros to represent new maximum extent counts for data/attr forks

Chandan Babu R
2022-03-05T12:44:40Z

On 04 Mar 2022 at 08:02, Dave Chinner wrote:
> On Tue, Mar 01, 2022 at 04:09:32PM +0530, Chandan Babu R wrote:
>> This commit defines new macros to represent maximum extent counts allowed by
>> filesystems which have support for large per-inode extent counters.
>>
>> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
>> Signed-off-by: Chandan Babu R <chandan.babu@oracle.com>
>> ---
>> fs/xfs/libxfs/xfs_bmap.c | 8 +++-----
>> fs/xfs/libxfs/xfs_bmap_btree.c | 2 +-
>> fs/xfs/libxfs/xfs_format.h | 20 ++++++++++++++++----
>> fs/xfs/libxfs/xfs_inode_buf.c | 3 ++-
>> fs/xfs/libxfs/xfs_inode_fork.c | 2 +-
>> fs/xfs/libxfs/xfs_inode_fork.h | 19 +++++++++++++++----
>> 6 files changed, 38 insertions(+), 16 deletions(-)
>>
>> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
>> index a01d9a9225ae..be7f8ebe3cd5 100644
>> --- a/fs/xfs/libxfs/xfs_bmap.c
>> +++ b/fs/xfs/libxfs/xfs_bmap.c
>> @@ -61,10 +61,8 @@ xfs_bmap_compute_maxlevels(
>> int sz; /* root block size */
>>
>> /*
>> - * The maximum number of extents in a file, hence the maximum number of
>> - * leaf entries, is controlled by the size of the on-disk extent count,
>> - * either a signed 32-bit number for the data fork, or a signed 16-bit
>> - * number for the attr fork.
>> + * The maximum number of extents in a fork, hence the maximum number of
>> + * leaf entries, is controlled by the size of the on-disk extent count.
>> *
>> * Note that we can no longer assume that if we are in ATTR1 that the
>> * fork offset of all the inodes will be
>> @@ -74,7 +72,7 @@ xfs_bmap_compute_maxlevels(
>> * ATTR2 we have to assume the worst case scenario of a minimum size
>> * available.
>> */
>> - maxleafents = xfs_iext_max_nextents(whichfork);
>> + maxleafents = xfs_iext_max_nextents(xfs_has_nrext64(mp), whichfork);
>> if (whichfork == XFS_DATA_FORK)
>> sz = XFS_BMDR_SPACE_CALC(MINDBTPTRS);
>> else
>> diff --git a/fs/xfs/libxfs/xfs_bmap_btree.c b/fs/xfs/libxfs/xfs_bmap_btree.c
>> index 453309fc85f2..e8d21d69b9ff 100644
>> --- a/fs/xfs/libxfs/xfs_bmap_btree.c
>> +++ b/fs/xfs/libxfs/xfs_bmap_btree.c
>> @@ -611,7 +611,7 @@ xfs_bmbt_maxlevels_ondisk(void)
>> minrecs[1] = xfs_bmbt_block_maxrecs(blocklen, false) / 2;
>>
>> /* One extra level for the inode root. */
>> - return xfs_btree_compute_maxlevels(minrecs, MAXEXTNUM) + 1;
>> + return xfs_btree_compute_maxlevels(minrecs, XFS_MAX_EXTCNT_DATA_FORK) + 1;
>> }
>>
>> /*
>> diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
>> index 9934c320bf01..d3dfd45c39e0 100644
>> --- a/fs/xfs/libxfs/xfs_format.h
>> +++ b/fs/xfs/libxfs/xfs_format.h
>> @@ -872,10 +872,22 @@ enum xfs_dinode_fmt {
>>
>> /*
>> * Max values for extlen, extnum, aextnum.
>> - */
>> -#define MAXEXTLEN ((xfs_extlen_t)0x001fffff) /* 21 bits */
>> -#define MAXEXTNUM ((xfs_extnum_t)0x7fffffff) /* signed int */
>> -#define MAXAEXTNUM ((xfs_aextnum_t)0x7fff) /* signed short */
>> + *
>> + * The newly introduced data fork extent counter is a 64-bit field. However, the
>> + * maximum number of extents in a file is limited to 2^54 extents (assuming one
>> + * blocks per extent) by the 54-bit wide startoff field of an extent record.
>> + *
>> + * A further limitation applies as shown below,
>> + * 2^63 (max file size) / 64k (max block size) = 2^47
>> + *
>> + * Rounding up 47 to the nearest multiple of bits-per-byte results in 48. Hence
>> + * 2^48 was chosen as the maximum data fork extent count.
>> + */
>> +#define MAXEXTLEN ((xfs_extlen_t)((1ULL << 21) - 1)) /* 21 bits */
>> +#define XFS_MAX_EXTCNT_DATA_FORK ((xfs_extnum_t)((1ULL << 48) - 1)) /* Unsigned 48-bits */
>> +#define XFS_MAX_EXTCNT_ATTR_FORK ((xfs_extnum_t)((1ULL << 32) - 1)) /* Unsigned 32-bits */
>> +#define XFS_MAX_EXTCNT_DATA_FORK_OLD ((xfs_extnum_t)((1ULL << 31) - 1)) /* Signed 32-bits */
>> +#define XFS_MAX_EXTCNT_ATTR_FORK_OLD ((xfs_extnum_t)((1ULL << 15) - 1)) /* Signed 16-bits */
>
> These go way beyond 80 columns. You do not need the trailing comment
> saying how many bits are supported - that's obvious from numbers.
> If you need to describe the actual supported limits, then do it
> in the head comment:
>
> /*
> * Max values for extent sizes and counts
> *
> * The original on-disk extent counts were held in signed fields,
> * resulting in maximum extent counts of 2^31 and 2^15 for the data
> * and attr forks respectively. Similarly the maximum extent length
> * is limited to 2^21 blocks by the 21-bit wide blockcount field of
> * a BMBT extent record.
> *
> * The newly introduced data fork extent counter can hold a 64-bit
> * value, however the maximum number of extents in a file is also
> * limited to 2^54 extents by the 54-bit wide startoff field of a BMBT
> * extent record.
> *
> * It is further limited by the maximum supported file size
> * of 2^63 *bytes*. This leads to a maximum extent count for maximally sized
> * filesystem blocks (64kB) of:
> *
> * 2^63 bytes / 2^16 bytes per block = 2^47 blocks
> *
> * Rounding up 47 to the nearest multiple of bits-per-byte
> * results in 48. Hence 2^48 was chosen as the maximum data fork
> * extent count.
> */
> #define MAXEXTLEN ((xfs_extlen_t)((1ULL << 21) - 1))
> #define XFS_MAX_EXTCNT_DATA_FORK ((xfs_extnum_t)((1ULL << 48) - 1))
> #define XFS_MAX_EXTCNT_ATTR_FORK ((xfs_extnum_t)((1ULL << 32) - 1))
> #define XFS_MAX_EXTCNT_DATA_FORK_OLD ((xfs_extnum_t)((1ULL << 31) - 1))
> #define XFS_MAX_EXTCNT_ATTR_FORK_OLD ((xfs_extnum_t)((1ULL << 15) - 1))
>

Ok. I will make the change suggested above.

>
> Hmmm. On reading that back and looking at the code below, maybe the
> names should be _LARGE and _SMALL, not (blank) and _OLD....
>

Ok. I will make this change.

>> /*
>> * Inode minimum and maximum sizes.
>> diff --git a/fs/xfs/libxfs/xfs_inode_buf.c b/fs/xfs/libxfs/xfs_inode_buf.c
>> index 860d32816909..34f360a38603 100644
>> --- a/fs/xfs/libxfs/xfs_inode_buf.c
>> +++ b/fs/xfs/libxfs/xfs_inode_buf.c
>> @@ -361,7 +361,8 @@ xfs_dinode_verify_fork(
>> return __this_address;
>> break;
>> case XFS_DINODE_FMT_BTREE:
>> - max_extents = xfs_iext_max_nextents(whichfork);
>> + max_extents = xfs_iext_max_nextents(xfs_dinode_has_nrext64(dip),
>> + whichfork);
>
>> if (di_nextents > max_extents)
>> return __this_address;
>> break;
>> diff --git a/fs/xfs/libxfs/xfs_inode_fork.c b/fs/xfs/libxfs/xfs_inode_fork.c
>> index ce690abe5dce..a3a3b54f9c55 100644
>> --- a/fs/xfs/libxfs/xfs_inode_fork.c
>> +++ b/fs/xfs/libxfs/xfs_inode_fork.c
>> @@ -746,7 +746,7 @@ xfs_iext_count_may_overflow(
>> if (whichfork == XFS_COW_FORK)
>> return 0;
>>
>> - max_exts = xfs_iext_max_nextents(whichfork);
>> + max_exts = xfs_iext_max_nextents(xfs_inode_has_nrext64(ip), whichfork);
>>
>> if (XFS_TEST_ERROR(false, ip->i_mount, XFS_ERRTAG_REDUCE_MAX_IEXTENTS))
>> max_exts = 10;
>> diff --git a/fs/xfs/libxfs/xfs_inode_fork.h b/fs/xfs/libxfs/xfs_inode_fork.h
>> index 4a8b77d425df..e56803436c61 100644
>> --- a/fs/xfs/libxfs/xfs_inode_fork.h
>> +++ b/fs/xfs/libxfs/xfs_inode_fork.h
>> @@ -133,12 +133,23 @@ static inline int8_t xfs_ifork_format(struct xfs_ifork *ifp)
>> return ifp->if_format;
>> }
>>
>> -static inline xfs_extnum_t xfs_iext_max_nextents(int whichfork)
>> +static inline xfs_extnum_t xfs_iext_max_nextents(bool has_nrext64,
> has_large_extent_counts
>> + int whichfork)
>> {
>> - if (whichfork == XFS_DATA_FORK || whichfork == XFS_COW_FORK)
>> - return MAXEXTNUM;
>> + switch (whichfork) {
>> + case XFS_DATA_FORK:
>> + case XFS_COW_FORK:
>> + return has_nrext64 ? XFS_MAX_EXTCNT_DATA_FORK
>> + : XFS_MAX_EXTCNT_DATA_FORK_OLD;
>
> if (has_large_extent_counts)
> return XFS_MAX_EXTCNT_DATA_FORK_LARGE;
> return XFS_MAX_EXTCNT_DATA_FORK_SMALL;
>
> That reads much better to me...
>

Ok.

--
chandan