On Tue, Jan 16, 2018 at 11:16 AM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > On Thu, Jan 4, 2018 at 6:20 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote: >> Lookup overlay inode in cache by origin inode, so we can decode a file >> handle of an open file even if the index has a whiteout index entry to >> mark this overlay inode was unlinked. >> >> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx> >> --- >> fs/overlayfs/export.c | 22 ++++++++++++++++++++-- >> fs/overlayfs/inode.c | 16 ++++++++++++++++ >> fs/overlayfs/overlayfs.h | 1 + >> 3 files changed, 37 insertions(+), 2 deletions(-) >> >> diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c >> index 602bada474ba..6ecb54d4b52c 100644 >> --- a/fs/overlayfs/export.c >> +++ b/fs/overlayfs/export.c >> @@ -385,13 +385,21 @@ static struct dentry *ovl_lower_fh_to_d(struct super_block *sb, >> struct ovl_path *stack = &origin; >> struct dentry *dentry = NULL; >> struct dentry *index = NULL; >> + struct inode *inode = NULL; >> + bool is_deleted = false; >> int err; >> >> /* First lookup indexed upper by fh */ > > Why not first look up origin, then look up ovl inode by origin? It > seems a faster path than going through the index first. Obviously if > icache lookup fails then we need to look up index, but the common case > will the cached one, so that should be the fast one, no? > Not really, because we do not know if the file handle is dir or non-dir. If file handle is dir than decode of file handle is expensive and can reduce worst case from two file handle decodes to just one: For lower dir: - one index lookup fails - one lower dir decode - one icache lookup - maybe one ovl_lookup_real(is_upper=false) For copied up indexed dir: - one index lookup success - one upper dir decode - one ovl_lookup_real(is_upper=true) That method avoids the origin dir decode for upper indexed dir at the cost of not looking for the decoded dir in icache. How about this as in idea: hash overlay inodes for NFS export by origin fh instead of by origin inode pointer. We can also avoid the "lookup index first" for non-dir if we set a flag OVL_FH_FLAG_CONNECTABLE on exported dir file handle, but my thinking was trying to keep the first version simple with as fewer special cases as possible. Thanks, Amir.
