On Wed, Jun 30, 2021 at 08:51:50AM -0700, Darrick J. Wong wrote: > On Mon, Jun 14, 2021 at 11:58:13AM +0530, Ritesh Harjani wrote: > > Test generic/020 fails for ext4 with 64K blocksize. So increase some overhead > > value to reduce the MAX_ATTRS so that it can accomodate for 64K blocksize. > > > > Signed-off-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx> > > --- > > common/attr | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/common/attr b/common/attr > > index d3902346..e8661d80 100644 > > --- a/common/attr > > +++ b/common/attr > > @@ -260,7 +260,7 @@ xfs|udf|pvfs2|9p|ceph|nfs) > > # Assume max ~1 block of attrs > > BLOCK_SIZE=`_get_block_size $TEST_DIR` > > # user.attribute_XXX="value.XXX" is about 32 bytes; leave some overhead > > - let MAX_ATTRS=$BLOCK_SIZE/40 > > + let MAX_ATTRS=$BLOCK_SIZE/48 > > 50% is quite a lot of overhead; maybe we should special-case this? The problem is that 32 bytes is an underestimate when i > 99 for user.attribute_$i=value_$i. And with a 4k blocksize, MAX_ATTRS = 4096 / 40 = 102. The exact calculation for ext4 is: fixed_block_overhead = 32 fixed_entry_overhead = 16 max_attr = (block_size - fixed_block_overhead) / (fixed_entry_overhead + round_up(len(attr_name), 4) + round_up(len(value), 4)) For 4k blocksizes, most of the attributes have an attr_name of "attribute_NN" which is 8, and "value_NN" which is 12. But for larger block sizes, we start having extended attributes of the form "attribute_NNN" or "attribute_NNNN", and "value_NNN" and "value_NNNN", which causes the round(len(..), 4) to jump up by 4 bytes. So round_up(len(attr_name, 4)) becomes 12 instead of 8, and round_up(len(value, 4)) becomes 16 instead of 12. So: max_attrs = (block_size - 32) / (16 + 12 + 16) or max_attrs = (block_size - 32) / 44 instead of: max_attrs = (block_size - 32) / (16 + 8 + 12) or max_attrs = (block_size - 32) / 36 So special casing things for block sizes > 4k may very well make sense. Perhaps it's even worth it to put in an ext[234] specific, exalc calculation for MAX_ATTRS in common/attr. Cheers, - Ted
