On Thu, 2022-02-24 at 09:15 -0500, Benjamin Coddington wrote:
> On 23 Feb 2022, at 16:12, trondmy@xxxxxxxxxx wrote:
>
> > From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
> >
> > Instead of relying on counting the page offsets as we walk through
> > the
> > page cache, switch to calculating them algorithmically.
> >
> > Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
> > ---
> > fs/nfs/dir.c | 18 +++++++++++++-----
> > 1 file changed, 13 insertions(+), 5 deletions(-)
> >
> > diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> > index 8f17aaebcd77..f2258e926df2 100644
> > --- a/fs/nfs/dir.c
> > +++ b/fs/nfs/dir.c
> > @@ -248,17 +248,20 @@ static const char
> > *nfs_readdir_copy_name(const
> > char *name, unsigned int len)
> > return ret;
> > }
> >
> > +static size_t nfs_readdir_array_maxentries(void)
> > +{
> > + return (PAGE_SIZE - sizeof(struct nfs_cache_array)) /
> > + sizeof(struct nfs_cache_array_entry);
> > +}
> > +
>
> Why the choice to use a runtime function call rather than the
> compiler's
> calculation? I suspect that the end result is the same, as the
> compiler
> will optimize it away, but I'm curious if there's a good reason for
> this.
>
The comparison is more efficient because no pointer arithmetic is
needed. As you said, the above function always evaluates to a constant,
and the array->size has been pre-calculated.
--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@xxxxxxxxxxxxxxx
