Re: [PATCH v1 4/4] page_reporting: change PAGE_REPORTING_DEFAULT_ORDER to -1

[Yuvraj Sakshith <yuvraj.sakshith@oss.qualcomm.com>]

On Fri, Feb 27, 2026 at 09:50:15PM +0100, David Hildenbrand (Arm) wrote:
> On 2/27/26 15:06, Yuvraj Sakshith wrote:
> > PAGE_REPORTING_DEFAULT_ORDER is now set to zero. This means,
> > pages of order zero cannot be reported to a client/driver -- as zero
> > is used to signal a fallback to MAX_PAGE_ORDER.
> > 
> > Change PAGE_REPORTING_DEFAULT_ORDER to (-1),
> > so that zero can be used as a valid order with which pages can
> > be reported.
> > 
> > Signed-off-by: Yuvraj Sakshith <yuvraj.sakshith@oss.qualcomm.com>
> > ---
> >  include/linux/page_reporting.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/page_reporting.h b/include/linux/page_reporting.h
> > index a7e3e30f2..3eb3e26d8 100644
> > --- a/include/linux/page_reporting.h
> > +++ b/include/linux/page_reporting.h
> > @@ -7,7 +7,7 @@
> >  
> >  /* This value should always be a power of 2, see page_reporting_cycle() */
> >  #define PAGE_REPORTING_CAPACITY		32
> > -#define PAGE_REPORTING_DEFAULT_ORDER	0
> > +#define PAGE_REPORTING_DEFAULT_ORDER	(-1)
> 
> No need for the ().
> 
> Wondering whether we now also want to do in this patch:
> 
> 
> diff --git a/mm/page_reporting.c b/mm/page_reporting.c
> index f0042d5743af..d432aadf9d07 100644
> --- a/mm/page_reporting.c
> +++ b/mm/page_reporting.c
> @@ -11,8 +11,7 @@
>  #include "page_reporting.h"
>  #include "internal.h"
> 
> -/* Initialize to an unsupported value */
> -unsigned int page_reporting_order = -1;
> +unsigned int page_reporting_order = PAGE_REPORTING_DEFAULT_ORDER;
> 
>  static int page_order_update_notify(const char *val, const struct
> kernel_param *kp)
>  {
> @@ -369,7 +368,7 @@ int page_reporting_register(struct
> page_reporting_dev_info *prdev)
>          * pageblock_order.
>          */
> 
> -       if (page_reporting_order == -1) {
> +       if (page_reporting_order == PAGE_REPORTING_DEFAULT_ORDER) {
> 
> 

Sure. Now that I think of it, don’t you think the first nested if() will
always be false? and can be compressed down to just one if()?

-       if (page_reporting_order == PAGE_REPORTING_DEFAULT_ORDER) {
-               if (prdev->order != PAGE_REPORTING_DEFAULT_ORDER &&
-                       prdev->order <= MAX_PAGE_ORDER)
-                       page_reporting_order = prdev->order;
-               else
-                       page_reporting_order = pageblock_order;
-       }
+       page_reporting_order = pageblock_order;
+
+       if (prdev->order != PAGE_REPORTING_DEFAULT_ORDER &&
+               prdev->order <= MAX_PAGE_ORDER)
+               page_reporting_order = prdev->order;

Thanks,
Yuvraj

> 
> (and wondering whether we should have called it
> PAGE_REPORTING_USE_DEFAULT_ORDER to make it clearer that it is not an
> actual order. Leaving that up to you :) )
> 
> -- 
> Cheers,
> 
> David