On 05/12/2008 16:51, "Joshua Nicholas" <jnicholas@xxxxxxxxxxxxxxx> wrote:
> Also in netback.c in net_tx_action_dealloc() after make_tx_response() I see:
>
> /* Ready for next use. */
> gnttab_reset_grant_page()
>
> Sure this resets the page_mapcount() back to 0, but it also
> sets the page_count() to 1 regardless of the current value.
>
> QUESTION 2: Why does the page_count() have to be set to 1?
A page is only acted on by net_tx_action_dealloc() after it is queued by
netif_page_release(), and that is called from free_pages(), which means
page_count() must be zero at that time (i.e., page is unused).
gnttab_reset_grant_page() is simply setting up the page for its next use.
If the page is *not* actually finished with by the net or blocks layers,
that would be very bad indeed. :-)
 -- Keir
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