Re: [PATCH 10/11] mm/zsmalloc: Handle single object charge migration in migrate_zspage

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

Hi Joshua,

kernel test robot noticed the following build warnings:

[auto build test WARNING on axboe/for-next]
[also build test WARNING on linus/master v7.0-rc3]
[cannot apply to akpm-mm/mm-everything next-20260311]
[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/Joshua-Hahn/mm-zsmalloc-Rename-zs_object_copy-to-zs_obj_copy/20260312-035531
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux.git for-next
patch link:    https://lore.kernel.org/r/20260311195153.4013476-11-joshua.hahnjy%40gmail.com
patch subject: [PATCH 10/11] mm/zsmalloc: Handle single object charge migration in migrate_zspage
config: arc-randconfig-001-20260312 (https://download.01.org/0day-ci/archive/20260312/202603121115.dm3Z6KvA-lkp@intel.com/config)
compiler: arc-linux-gcc (GCC) 8.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260312/202603121115.dm3Z6KvA-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/202603121115.dm3Z6KvA-lkp@intel.com/

All warnings (new ones prefixed by >>):

   mm/zsmalloc.c: In function 'zs_compact.part.28':
>> mm/zsmalloc.c:1696:15: warning: 's_idx' is used uninitialized in this function [-Wuninitialized]
     unsigned int s_idx, d_idx;
                  ^~~~~


vim +/s_idx +1696 mm/zsmalloc.c

  1686	
  1687	#ifdef CONFIG_MEMCG
  1688	static void zs_migrate_objcg(struct zspage *s_zspage, struct zspage *d_zspage,
  1689				     unsigned long used_obj, unsigned long free_obj,
  1690				     struct zs_pool *pool, int size)
  1691	{
  1692		struct zpdesc *s_zpdesc, *d_zpdesc;
  1693		struct obj_cgroup *objcg;
  1694		struct mem_cgroup *memcg;
  1695		struct lruvec *l;
> 1696		unsigned int s_idx, d_idx;
  1697		unsigned int s_off, d_off;
  1698		int charges[4], nids[4], partial;
  1699		int s_bytes_in_page, d_bytes_in_page;
  1700		int i;
  1701	
  1702		if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
  1703			goto out;
  1704	
  1705		obj_to_location(used_obj, &s_zpdesc, &s_idx);
  1706		obj_to_location(free_obj, &d_zpdesc, &d_idx);
  1707	
  1708		objcg = s_zspage->objcgs[s_idx];
  1709		if (!objcg)
  1710			goto out;
  1711	
  1712		/*
  1713		 * The object migration here can touch up to 4 nodes.
  1714		 * Instead of breaking down all possible combinations of node changes,
  1715		 * just uncharge entirely from the source and charge entirely to the
  1716		 * destination, even if there is are node overlaps between src and dst.
  1717		 */
  1718		s_off = (s_idx * size) % PAGE_SIZE;
  1719		d_off = (d_idx * size) % PAGE_SIZE;
  1720		s_bytes_in_page = min_t(int, size, PAGE_SIZE - s_off);
  1721		d_bytes_in_page = min_t(int, size, PAGE_SIZE - d_off);
  1722	
  1723		charges[0] = -s_bytes_in_page;
  1724		nids[0] = page_to_nid(zpdesc_page(s_zpdesc));
  1725		charges[1] = -(size - s_bytes_in_page); /* 0 if object doesn't span */
  1726		if (charges[1])
  1727			nids[1] = page_to_nid(zpdesc_page(get_next_zpdesc(s_zpdesc)));
  1728	
  1729		charges[2] = d_bytes_in_page;
  1730		nids[2] = page_to_nid(zpdesc_page(d_zpdesc));
  1731		charges[3] = size - d_bytes_in_page; /* 0 if object doesn't span */
  1732		if (charges[3])
  1733			nids[3] = page_to_nid(zpdesc_page(get_next_zpdesc(d_zpdesc)));
  1734	
  1735		rcu_read_lock();
  1736		memcg = obj_cgroup_memcg(objcg);
  1737		for (i = 0; i < 4; i++) {
  1738			if (!charges[i])
  1739				continue;
  1740	
  1741			l = mem_cgroup_lruvec(memcg, NODE_DATA(nids[i]));
  1742			partial = (PAGE_SIZE * charges[i]) / size;
  1743			mod_memcg_lruvec_state(l, pool->compressed_stat, charges[i]);
  1744			mod_memcg_lruvec_state(l, pool->uncompressed_stat, partial);
  1745		}
  1746		rcu_read_unlock();
  1747	
  1748		dec_node_page_state(zpdesc_page(s_zpdesc), pool->uncompressed_stat);
  1749		inc_node_page_state(zpdesc_page(d_zpdesc), pool->uncompressed_stat);
  1750	
  1751	out:
  1752		d_zspage->objcgs[d_idx] = s_zspage->objcgs[s_idx];
  1753		s_zspage->objcgs[s_idx] = NULL;
  1754	}
  1755	#else
  1756	static void zs_migrate_objcg(struct zspage *s_zspage, struct zspage *d_zspage,
  1757				     unsigned long used_obj, unsigned long free_obj,
  1758				     struct zs_pool *pool, int size)
  1759	{
  1760	}
  1761	#endif
  1762	

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