tmpfs use of wired_count

[Alan Cox]

On Wed, Jun 30, 2010 at 11:33 AM, Jeseem S <jeseems at gmail.com> wrote:

> hi,
>   I am a newbie on freebsd kernel. Am currently trying to debug a scenario,
> where a custom driver I load uses a lot of static memory and hence lots of
> wired pages.
> The system still has a lot of free memory ( more than 200MB) and a free
> swap
> space ( > 500MB).
> Once I load the driver, the tmpfs loaded on /tmp shows a size of 0.
>
> in tmpfs/tmpfs.h, I see that the free memory available is reduced by number
> of wired pages ( see code below).
> Is this correct logic  ? why do we need to reduce wired count from free
> pages available ?
>
>
No, it doesn't appear correct.  Moreover, it's also incorrect that
cnt.v_cache_count isn't included in the initial calculation of size.

Regards,
Alan



>
> /*
>  * Returns information about the number of available memory pages,
>  * including physical and virtual ones.
>  *
>  * If 'total' is TRUE, the value returned is the total amount of memory
>  * pages configured for the system (either in use or free).
>  * If it is FALSE, the value returned is the amount of free memory pages.
>  *
>  * Remember to remove TMPFS_PAGES_RESERVED from the returned value to avoid
>  * excessive memory usage.
>  *
>  */
> static __inline size_t
> tmpfs_mem_info(void)
> {
>        size_t size;
>
>        size = swap_pager_avail + cnt.v_free_count + cnt.v_inactive_count;
>        size -= size > cnt.v_wire_count ? cnt.v_wire_count : size;
>        return size;
> }
>
>
> Thanks
> Jeseem
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