Re: [PATCH][5/8] proc: export mlocked pages info through "/proc/meminfo: Wired"

[Dave Hansen <haveblue@us.ibm.com>]

On Mon, 2006-03-20 at 08:37 -0500, Stone Wang wrote:
> --- linux-2.6.15.orig/include/linux/mm.h        2006-01-02 22:21:10.000000000 -0500
> +++ linux-2.6.15/include/linux/mm.h     2006-03-07 01:49:12.000000000 -0500
> @@ -218,6 +221,10 @@
>         unsigned long flags;            /* Atomic flags, some possibly
>                                          * updated asynchronously */
>         atomic_t _count;                /* Usage count, see below. */
> +       unsigned short wired_count; /* Count of wirings of the page.
> +                                        * If not zero,the page would be SetPageWired,
> +                                        * and put on Wired list of the zone.
> +                                        */
>         atomic_t _mapcount;             /* Count of ptes mapped in mms,
>                                          * to show when page is mapped
>                                          * & limit reverse map searches. 

We're usually pretty picky about adding stuff to 'struct page'.  It
_just_ fits inside a cacheline on most 32-bit architectures.  

Can this wired_count not be derived at runtime?  It seems like it would
be possible to run through all VMAs mapping the page, and determining
how many of them are VM_LOCKED.  Would that be too slow?

Also, does it matter how many times it is locked, or just that
_somebody_ has it locked?  

-- Dave

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