[LU-16581] osd_xattr_get() is much more expensive with zfs

Mon, 20 Feb 2023 20:21:45 +0000

just noticed that sanity/103e takes significantly longer with ZFS. there are number of contributors, but I found one especially interesting:
ldiskfs:

attr_get                  36535 samples [usecs] 0 80 1085 9093

zfs:

attr_get                  36537 samples [usecs] 0 20790 750797 1636365521

i.e. osd_attr_get() (called on a directory) is 692 times slower than ldiskfs version.

it's used only in mdt_attr_get_internal():

		if (ma->ma_attr.la_dirent_count != LU_DIRENT_COUNT_UNSET &&
		    ma->ma_attr.la_dirent_count >
			mdt->mdt_restriper.mdr_dir_split_count &&
		    !fid_is_root(mdt_object_fid(o)) &&
		    mdt->mdt_enable_dir_auto_split &&
		    !o->mot_restriping &&
		    stripe_count < atomic_read(&mdt->mdt_mds_mds_conns) + 1 &&
		    !fixed_layout)
			mdt_auto_split_add(info, o);

and only to check whether (re)striping is needed.
I find it suboptimal that:

OSD needs to calculate la_dirent_count for every directory
we do this every getattr

Whamcloud Community JIRA

[LU-16581] osd_xattr_get() is much more expensive with zfs