Re: [RFC PATCH 1/1] mm: vmscan: keep anon scanning enabled when swapcache folios are present

Re: [RFC PATCH 1/1] mm: vmscan: keep anon scanning enabled when swapcache folios are present

[kernel test robot]

Hi Thomas,

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

[auto build test ERROR on akpm-mm/mm-everything]
[also build test ERROR on linus/master v7.1-rc1 next-20260430]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Thomas-Hellstr-m/mm-vmscan-keep-anon-scanning-enabled-when-swapcache-folios-are-present/20260428-183540
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20260427103532.5623-2-thomas.hellstrom%40linux.intel.com
patch subject: [RFC PATCH 1/1] mm: vmscan: keep anon scanning enabled when swapcache folios are present
config: arm-allnoconfig (https://download.01.org/0day-ci/archive/20260502/202605021047.kY1JeLwn-lkp@intel.com/config)
compiler: clang version 23.0.0git (https://github.com/llvm/llvm-project 5bac06718f502014fade905512f1d26d578a18f3)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260502/202605021047.kY1JeLwn-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/202605021047.kY1JeLwn-lkp@intel.com/

All errors (new ones prefixed by >>):

>> mm/vmscan.c:365:38: error: use of undeclared identifier 'NR_SWAPCACHE'
     365 |         if (node_page_state(NODE_DATA(nid), NR_SWAPCACHE) > 0)
         |                                             ^~~~~~~~~~~~
   1 error generated.


vim +/NR_SWAPCACHE +365 mm/vmscan.c

   341	
   342	static inline bool can_reclaim_anon_pages(struct mem_cgroup *memcg,
   343						  int nid,
   344						  struct scan_control *sc)
   345	{
   346		if (memcg == NULL) {
   347			/*
   348			 * For non-memcg reclaim, is there
   349			 * space in any swap device?
   350			 */
   351			if (get_nr_swap_pages() > 0)
   352				return true;
   353		} else {
   354			/* Is the memcg below its swap limit? */
   355			if (mem_cgroup_get_nr_swap_pages(memcg) > 0)
   356				return true;
   357		}
   358	
   359		/*
   360		 * Even with no free swap slots, anon folios already in the swap cache
   361		 * carry a pre-allocated slot and can be written back and freed from RAM
   362		 * without consuming a new one.  Do not suppress anon scanning when such
   363		 * folios are present on this node.
   364		 */
 > 365		if (node_page_state(NODE_DATA(nid), NR_SWAPCACHE) > 0)
   366			return true;
   367	
   368		/*
   369		 * The page can not be swapped.
   370		 *
   371		 * Can it be reclaimed from this node via demotion?
   372		 */
   373		return can_demote(nid, sc, memcg);
   374	}
   375	

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