On Thu, Mar 21, 2024 at 11:50:36AM +0100, Vlastimil Babka wrote: > Yeah I think we could keep that logic. I am all for keeping it. > But we could also simply subtract the refcount of the old handle (the > "allocated for migration") in __folio_copy_owner() no? Then we wouldn't need > the extra migrate_handle. Since new_page will have the old handle pointing to the old stack after the call, we could uncharge the old_page to the migrate_stack, which new_page->_handle holds before it gets changed. So we basically swap it. It could work, but I kinda have a bittersweet feeling here. I am trying to work towards to reduce the number of lookups in the hlist, but for the approach described above I would need to lookup the stack for new_page->handle in order to substract the page. OTHO, I understand that adding migrate_handle kinda wasted memory. 16MB for 16GB of memory. > Also we might have more issues here. Most page owner code takes care to set > everything for all pages within a folio, but __folio_copy_owner() and > __set_page_owner_migrate_reason() don't. I did not check deeply but do not we split the folio upon migration in case it is large? Which means we should reach split_page_owner() before the copy takes place. Do I get it right? -- Oscar Salvador SUSE Labs
