Re: [PATCH RFC 5/9] mm/page_owner: add swap hooks

[kernel test robot <lkp@intel.com>]

Hi Mauricio,

[This is a private test report for your RFC patch.]
kernel test robot noticed the following build warnings:

[auto build test WARNING on akpm-mm/mm-everything]

url:    https://github.com/intel-lab-lkp/linux/commits/Mauricio-Faria-de-Oliveira/mm-add-config-option-SWAP_PAGE_OWNER/20251206-072021
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20251205231721.104505-6-mfo%40igalia.com
patch subject: [PATCH RFC 5/9] mm/page_owner: add swap hooks
config: x86_64-allmodconfig (https://download.01.org/0day-ci/archive/20251208/202512080831.Fl7k0uXy-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251208/202512080831.Fl7k0uXy-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202512080831.Fl7k0uXy-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> mm/page_owner.c:593:7: warning: variable 'i' set but not used [-Wunused-but-set-variable]
     593 |         long i = 0, nr_pages = folio_nr_pages(folio);
         |              ^
   1 warning generated.


vim +/i +593 mm/page_owner.c

   584	
   585	/* Load the initial stack information from xarray to page_owner. */
   586	void __page_owner_swap_restore(swp_entry_t entry, struct folio *folio)
   587	{
   588		struct page_ext_iter iter;
   589		struct page_ext *page_ext;
   590		struct page_owner *page_owner;
   591		struct swap_page_owner *spo;
   592		depot_stack_handle_t handle = 0;
 > 593		long i = 0, nr_pages = folio_nr_pages(folio);
   594	
   595		rcu_read_lock();
   596		for_each_page_ext(&folio->page, nr_pages, page_ext, iter) {
   597			spo = (struct swap_page_owner *) load_swap_page_owner(entry);
   598			if (!spo) {
   599				rcu_read_unlock();
   600				return;
   601			}
   602	
   603			page_owner = get_page_owner(page_ext);
   604			copy_from_swap_page_owner(page_owner, spo);
   605	
   606			if (!handle)
   607				handle = page_owner->handle;
   608			i++;
   609			entry.val++;
   610		}
   611		rcu_read_unlock();
   612	
   613		/*
   614		 * Fix-up: decrement refcount of the swap-in allocation.
   615		 * It was incremented by the page-alloc at swap-in.
   616		 * (early_handle: see __reset_page_owner().)
   617		 *
   618		 * FIXME(mfo): 'dec_stack_record_count: refcount went to 0 ...'
   619		 * with stack_depot oops is hit occasionaly on tests or shutdown.
   620		 */
   621		if (handle != early_handle)
   622			dec_stack_record_count(handle, nr_pages);
   623	}
   624	

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