Re: deferred rss update instead of sloppy rss

[Nick Piggin]

Linus Torvalds wrote:
> On Mon, 22 Nov 2004, Christoph Lameter wrote:
>
> > The problem is then that the proc filesystem must do an extensive scan
> > over all threads to find users of a certain mm_struct.
>
>
> The alternative is to just add a simple list into the task_struct and the
> head of it into mm_struct. Then, at fork, you just finish the fork() with
>
> 	list_add(p->mm_list, p->mm->thread_list);
>
> and do the proper list_del() in exit_mm() or wherever.
>
> You'll still loop in /proc, but you'll do the minimal loop necessary.

Yes, that was what I was thinking we'd have to resort to. Not a bad idea.

It would be nice if you could have it integrated with the locking that
is already there - for example mmap_sem, although that might mean you'd
have to take mmap_sem for writing which may limit scalability of thread
creation / destruction... maybe a seperate lock / semaphore for that list
itself would be OK.

Deferred rss might be a practical solution, but I'd prefer this if it can
be made workable.

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