Re: hashed waitqueues

[Andrew Morton <akpm@zip.com.au>]

William Lee Irwin III wrote:
> 
> This is a long-discussed space optimization for the VM system, with
> what is expected to be a minor time tradeoff.

Nice code.

> ...
> +       /*
> +        * Although the default semantics of wake_up() are
> +        * to wake all, here the specific function is used
> +        * to make it even more explicit that a number of
> +        * pages are being waited on here.
> +        */
> +       if(waitqueue_active(page_waitqueue(page)))
> +               wake_up_all(page_waitqueue(page));

Does the compiler CSE these two calls to page_waitqueue()?
All versions?   I'd be inclined to do CSE-by-hand here.

Also, why wake_up_all()?  That will wake all tasks which are sleeping
in __lock_page(), even though they've asked for exclusive wakeup
semantics.  Will a bare wake_up() here not suffice?

-