Since the stacking of regular file operations [1], the overlayfs edition of write_iter() is called when writing regular files. Since then, xattr lookup is needed on every write since file_remove_privs() is called from ovl_write_iter(), which would become the performance bottleneck when writing small chunks of data. In my test case, file_remove_privs() would consume ~15% CPU when running fstime of unixbench (the workload is repeadly writing 1 KB to the same file) [2]. Inherit the SB_NOSEC flag from upperdir. Since then xattr lookup would be done only once on the first write. Unixbench fstime gets a ~20% performance gain with this patch. [1] https://lore.kernel.org/lkml/20180606150905.GC9426@magnolia/T/ [2] https://www.spinics.net/lists/linux-unionfs/msg07153.html Signed-off-by: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx> --- fs/overlayfs/super.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c index 732ad54..1934f71 100644 --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -1052,6 +1052,10 @@ static int ovl_get_upper(struct super_block *sb, struct ovl_fs *ofs, upper_mnt->mnt_flags &= ~(MNT_NOATIME | MNT_NODIRATIME | MNT_RELATIME); ofs->upper_mnt = upper_mnt; + /* inherit SB_NOSEC flag from upperdir */ + if (upper_mnt->mnt_sb->s_flags & SB_NOSEC) + sb->s_flags |= SB_NOSEC; + if (ovl_inuse_trylock(ofs->upper_mnt->mnt_root)) { ofs->upperdir_locked = true; } else { -- 1.8.3.1
