On Mon, 24 Jul 2006 18:20:00 -0700
Andrew Morton <[email protected]> wrote:
>
> It allocates a potentially-significant amount of memory per-task, until
> that tasks exits (we could release it earlier, but the problem remains) and
> it adds yet another global lock in the process exit path.
>
I see.
> > 5 files changed, 138 insertions(+), 62 deletions(-)
>
> And it adds complexity and code.
>
> So I think we're still seeking a solution to this.
>
> Options might be:
>
> a) Pin the most-recently-visited task in some manner, so that it is
> still on the global task list when we return. That's fairly simple to
> do (defer the release_task()) but it affects task lifetime and visibility
> in rare and worrisome ways.
>
> b) Change proc_pid_readdir() so that it walks the pid_hash[] array
> instead of the task list. Need to do something clever when traversing
> each bucket's list, but I'm not sure what ;) It's the same problem.
>
> Possibly what we could do here is to permit the task which is walking
> /proc to pin a particular `struct pid': take a ref on it then when we
> next start walking one of the pid_hash[] chains, we _know_ that the
> `struct pid' which we're looking for will still be there. Even if it
> now refers to a departed process.
>
> c) Nuke the pid_hash[], convert the whole thing to a radix-tree.
> They're super-simple to traverse. Not sure what we'd index it by
> though.
>
> I guess b) is best.
>
I tried b) at the first place. but it was not very good because
proc_pid_readdir() has to traverse all pids, not tgids. So, I had to access
task_struct of the pid. I wanted to avoid to access task struct itself,
my patch implemented a table made only from tgids.
But as you say, my patch is much intrusive.
I'll dig this more. thank you for advise.
Thanks,
-Kame
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