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

[Gregory Price <gourry@gourry.net>]

On Thu, May 14, 2026 at 10:48:28AM -0400, Michael S. Tsirkin wrote:
> 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@redhat.com>
> > > 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.
> 

You do this exact thing again later :]

https://lore.kernel.org/linux-mm/9a22e0f9bbe1278913754db6df76e291a006181a.1778616612.git.mst@redhat.com/

~Gregory