Messages in this thread | | | Subject | Re: [RFC PATCH] fs: use a sequence counter instead of file_lock in fd_install | From | Eric Dumazet <> | Date | Thu, 16 Apr 2015 13:42:03 -0700 |
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On Thu, 2015-04-16 at 19:09 +0100, Al Viro wrote: > On Thu, Apr 16, 2015 at 02:16:31PM +0200, Mateusz Guzik wrote: > > @@ -165,8 +165,10 @@ static int expand_fdtable(struct files_struct *files, int nr) > > cur_fdt = files_fdtable(files); > > if (nr >= cur_fdt->max_fds) { > > /* Continue as planned */ > > + write_seqcount_begin(&files->fdt_seqcount); > > copy_fdtable(new_fdt, cur_fdt); > > rcu_assign_pointer(files->fdt, new_fdt); > > + write_seqcount_end(&files->fdt_seqcount); > > if (cur_fdt != &files->fdtab) > > call_rcu(&cur_fdt->rcu, free_fdtable_rcu); > > Interesting. AFAICS, your test doesn't step anywhere near that path, > does it? So basically you never hit the retries during that...
Right, but then the table is almost never changed for a given process, as we only increase it by power of two steps.
(So I scratch my initial comment, fdt_seqcount is really mostly read)
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