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 <[email protected]> > 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
