On Tue, Jun 09, 2026 at 01:44:37PM -0400, Gregory Price wrote: > On Tue, Jun 09, 2026 at 11:53:20AM -0400, Michael S. Tsirkin wrote: > > --- a/mm/page_reporting.c > > +++ b/mm/page_reporting.c > > @@ -174,10 +174,10 @@ page_reporting_cycle(struct page_reporting_dev_info > > *prdev, struct zone *zone, > > * list processed. This should result in us reporting all pages on > > * an idle system in about 30 seconds. > > * > > - * The division here should be cheap since PAGE_REPORTING_CAPACITY > > - * should always be a power of 2. > > + * The division here uses integer division; capacity need > > + * not be a power of 2. > > */ > > - budget = DIV_ROUND_UP(area->nr_free, PAGE_REPORTING_CAPACITY * 16); > > + budget = DIV_ROUND_UP(area->nr_free, prdev->capacity * 16); > > > > Initial look - is there a div-by-0 here? I noticed the old check > prevents this from being (0 * 16), but i don't see (on first pass) > the same check anywhere. > > Unless this line below always forces the above to be a > PAGE_REPORTING_CAPCAITY if it's set to 0.
It does, does it not? > > + if (!prdev->capacity || prdev->capacity > PAGE_REPORTING_CAPACITY) > > + prdev->capacity = PAGE_REPORTING_CAPACITY; > > + > > It's worth making this corner condition a little more obvious. > > The code intends for > > if (capacity == 0) > capacity = PAGE_REPORTING_CAPACITY > > but that's not reflected in the changelog as a default value. > > When happens if a driver sets (capacity=0) either on purpose (???) what would the purpose be? if you don't want reporting do not register. > or > because there's a bug (???) exactly ??? since where are we practicing defensive programming in kernel APIs? > and then page_reporting.c forces it up to > 32? > > There's something to improve here. > > ~Gregory So I'll update the commit log to mention PAGE_REPORTING_CAPACITY. And maybe a comment near capacity field? Should be enough? -- MST
