On Thu 06-04-23 23:06:21, Chao Yu wrote: > As Ted pointed out as below: > > " > However the minlen variable in ext4_trim_fs is in units of *clusters*. > And so it gets rounded up two places. The first time is when it is > converted into units of a cluster: > > minlen = EXT4_NUM_B2C(EXT4_SB(sb), > range->minlen >> sb->s_blocksize_bits); > > Oh, and by the way, that first conversion is not correct as currently > written in ext4_fs_trim(). It should be > > minlen = (range->minlen + EXT4_CLUSTER_SIZE(sb) - 1) >> > (sb->s_blocksize_bits + EXT4_CLUSTER_BITS(sb)); > " > > The reason is if range->minlen is smaller than block size of ext4, > original calculation "range->minlen >> sb->s_blocksize_bits" may > return zero, but since EXT4_NUM_B2C() expects a non-zero in-parameter, > so it needs to round up range->minlen to cluster size directly as above. > > Link: https://lore.kernel.org/lkml/20230311031843.GF860405@xxxxxxx/ > Suggested-by: Theodore Ts'o <tytso@xxxxxxx> > Signed-off-by: Chao Yu <chao@xxxxxxxxxx> Looks good to me. Feel free to add: Reviewed-by: Jan Kara <jack@xxxxxxx> Honza > --- > fs/ext4/mballoc.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c > index 5b2ae37a8b80..d8b9d6a83d1e 100644 > --- a/fs/ext4/mballoc.c > +++ b/fs/ext4/mballoc.c > @@ -6478,8 +6478,8 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range) > > start = range->start >> sb->s_blocksize_bits; > end = start + (range->len >> sb->s_blocksize_bits) - 1; > - minlen = EXT4_NUM_B2C(EXT4_SB(sb), > - range->minlen >> sb->s_blocksize_bits); > + minlen = (range->minlen + EXT4_CLUSTER_SIZE(sb) - 1) >> > + (sb->s_blocksize_bits + EXT4_CLUSTER_BITS(sb)); > > if (minlen > EXT4_CLUSTERS_PER_GROUP(sb) || > start >= max_blks || > -- > 2.25.1 > -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
