On Tue, Jan 16, 2018 at 10:37 AM, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > 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. Good idea. That way we can leave out the middleman (underlying fh decode) in the cached case. > 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. Not sure I understand. If cached lookup fails, then we do always need to try and lookup index first before falling back to decoding origin, right? Thanks, Miklos > > Thanks, > Amir.
