On Wed, Oct 21, 2015 at 02:18:30PM -0700, Eric Dumazet wrote:
> On Wed, 2015-10-21 at 18:04 +0200, casper....@oracle.com wrote:
>
> > It is only expensive within the process itself.
>
> thread synchro would require additional barriers to maintain this state,
> for a very unlikely case.
>
> The atomic_{inc|dec}() on file refcount are already a problem.
To be fair, this would avoid at least _that_ - file refcount updates would
be less frequent. However, unlike file->f_count, *descriptor* refcounts
would be much harder to keep in different cachelines.
> We certainly do not use/take a lock to find a file pointer into file
> descriptor table.
>
> (This lock is only used at open() or close() time)
as well as dup2() and friends, of course. But yes, we are pretty careful
about avoiding non-local stores on the normal "get file by descriptor" path -
in case of non-shared descriptor table we don't do them at all, and in case
of shared one we only modify refcount in struct file.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
