On 23.01.25 20:55, Matthew Wilcox wrote:
The page reference count tracepoints currently look like this:
__entry->pfn = page_to_pfn(page);
__entry->flags = page->flags;
__entry->count = page_ref_count(page);
__entry->mapcount = atomic_read(&page->_mapcount);
__entry->mapping = page->mapping;
__entry->mt = get_pageblock_migratetype(page);
TP_printk("pfn=0x%lx flags=%s count=%d mapcount=%d mapping=%p mt=%d val=%d",
Soon, pages will not have a ->mapping, nor a ->mapcount [1]. But they will
still have a refcount, at least for now. put_page() will move out of
line and look something like this:
void put_page(struct page *page)
{
unsigned long memdesc = page->memdesc;
if (memdesc_is_folio(memdesc))
return folio_put(memdesc_folio(memdesc));
BUG_ON(memdesc_is_slab(memdesc));
... handle other memdesc types here ...
if (memdesc_is_compound_head(memdesc))
page = memdesc_head_page(memdesc);
if (put_page_testzero(page))
__put_page(page);
}
What I'm thinking is:
- Define a set of folio_ref_* tracepoints which dump exactly the same info
as page_ref does today
- Remove mapping & mapcount from page_ref_* functions.
Yes, I did not completely remove the mapcount in
6eca32567455db2db38b1126e0d6ad8f0e5c3ed9, but likely I just should have.
We're dumping raw values of flags/mappings/mapcount right now, and
probably we should drop them all here.
I also once thought about introducing folio variants on my todo list to
dump actual per-folio fields instead of raw values.
One "problematic" part in the current usage are things like
page_ref_sub_and_test(), where we end up calling
__page_ref_mod_and_test() on something with a refcount of 0 (or could
even have been reallocated? not sure)
--
Cheers,
David / dhildenb
