Re: [PATCH v7 02/31] mm: page_alloc: propagate PageReported flag across buddy splits

[Michael S. Tsirkin]

On Thu, May 14, 2026 at 07:51:03AM -0400, Gregory Price wrote:
> On Tue, May 12, 2026 at 05:05:16PM -0400, Michael S. Tsirkin wrote:
> > When a reported free page is split via expand() to satisfy a
> > smaller allocation, the sub-pages placed back on the free lists
> > lose the PageReported flag.  This means they will be unnecessarily
> > re-reported to the hypervisor in the next reporting cycle, wasting
> > work.
> > 
> > While I was unable to quantify the performance difference, it is
> > an obvious waste, even if small.
> > 
> > Propagate the PageReported flag to sub-pages during expand(),
> > both in page_del_and_expand() and try_to_claim_block(), so
> > that they are recognized as already-reported.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > Assisted-by: Claude:claude-opus-4-6
> ... snip ...
> > @@ -1731,9 +1740,10 @@ static __always_inline void page_del_and_expand(struct zone *zone,
> >  						int high, int migratetype)
> >  {
> >  	int nr_pages = 1 << high;
> > +	bool was_reported = page_reported(page);
> >  
> >  	__del_page_from_free_list(page, zone, high, migratetype);
> > -	nr_pages -= expand(zone, page, low, high, migratetype);
> > +	nr_pages -= expand(zone, page, low, high, migratetype, was_reported);
> >  	account_freepages(zone, -nr_pages, migratetype);
> >  }
> >  
> 
> Maybe mildly out of scope but worth asking:  Are there other flags that
> should be retained/propogated on a split?  If so, rather than pass
> was_reported, should we just take a temporary copy of the page flags and
> pass them all in?
> 
> ~Gregory


Not that I can see, no.

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MST