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]. Set the MS_NOSEC flag for overlayfs superblock. 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 | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c index 732ad54..0b047ce 100644 --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -1817,7 +1817,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent) sb->s_magic = OVERLAYFS_SUPER_MAGIC; sb->s_xattr = ovl_xattr_handlers; sb->s_fs_info = ofs; - sb->s_flags |= SB_POSIXACL; + sb->s_flags |= (SB_POSIXACL | SB_NOSEC); err = -ENOMEM; root_dentry = ovl_get_root(sb, upperpath.dentry, oe); -- 1.8.3.1
