Re: [PATCH 6/8] mm: shmem: add mTHP support for anonymous shmem

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

Hi Baolin,

kernel test robot noticed the following build warnings:

[auto build test WARNING on akpm-mm/mm-everything]
[also build test WARNING on next-20240506]
[cannot apply to linus/master v6.9-rc7]
[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/Baolin-Wang/mm-move-highest_order-and-next_order-out-of-the-THP-config/20240506-164838
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/adc64bf0f150bdc614c6c06fc313adeef7dbbbff.1714978902.git.baolin.wang%40linux.alibaba.com
patch subject: [PATCH 6/8] mm: shmem: add mTHP support for anonymous shmem
config: s390-allnoconfig (https://download.01.org/0day-ci/archive/20240507/202405071820.2KY0UnDu-lkp@intel.com/config)
compiler: clang version 19.0.0git (https://github.com/llvm/llvm-project 0ab4458df0688955620b72cc2c72a32dffad3615)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240507/202405071820.2KY0UnDu-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/202405071820.2KY0UnDu-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from mm/shmem.c:28:
   In file included from include/linux/ramfs.h:5:
   In file included from include/linux/fs_parser.h:11:
   In file included from include/linux/fs_context.h:14:
   In file included from include/linux/security.h:33:
   In file included from include/linux/mm.h:2253:
   include/linux/vmstat.h:514:36: warning: arithmetic between different enumeration types ('enum node_stat_item' and 'enum lru_list') [-Wenum-enum-conversion]
     514 |         return node_stat_name(NR_LRU_BASE + lru) + 3; // skip "nr_"
         |                               ~~~~~~~~~~~ ^ ~~~
>> mm/shmem.c:1780:10: warning: variable 'folio' is used uninitialized whenever 'while' loop exits because its condition is false [-Wsometimes-uninitialized]
    1780 |                 while (suitable_orders) {
         |                        ^~~~~~~~~~~~~~~
   mm/shmem.c:1795:7: note: uninitialized use occurs here
    1795 |         if (!folio)
         |              ^~~~~
   mm/shmem.c:1780:10: note: remove the condition if it is always true
    1780 |                 while (suitable_orders) {
         |                        ^~~~~~~~~~~~~~~
         |                        1
   mm/shmem.c:1750:21: note: initialize the variable 'folio' to silence this warning
    1750 |         struct folio *folio;
         |                            ^
         |                             = NULL
   mm/shmem.c:1564:20: warning: unused function 'shmem_show_mpol' [-Wunused-function]
    1564 | static inline void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
         |                    ^~~~~~~~~~~~~~~
   3 warnings generated.


vim +1780 mm/shmem.c

  1741	
  1742	static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf,
  1743			gfp_t gfp, struct inode *inode, pgoff_t index,
  1744			struct mm_struct *fault_mm, bool huge, unsigned long orders)
  1745	{
  1746		struct address_space *mapping = inode->i_mapping;
  1747		struct shmem_inode_info *info = SHMEM_I(inode);
  1748		struct vm_area_struct *vma = vmf ? vmf->vma : NULL;
  1749		unsigned long suitable_orders;
  1750		struct folio *folio;
  1751		long pages;
  1752		int error, order;
  1753	
  1754		if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
  1755			huge = false;
  1756	
  1757		if (huge || orders > 0) {
  1758			if (vma && vma_is_anon_shmem(vma) && orders) {
  1759				suitable_orders = anon_shmem_suitable_orders(inode, vmf,
  1760								mapping, index, orders);
  1761			} else {
  1762				pages = HPAGE_PMD_NR;
  1763				suitable_orders = BIT(HPAGE_PMD_ORDER);
  1764				index = round_down(index, HPAGE_PMD_NR);
  1765	
  1766				/*
  1767				 * Check for conflict before waiting on a huge allocation.
  1768				 * Conflict might be that a huge page has just been allocated
  1769				 * and added to page cache by a racing thread, or that there
  1770				 * is already at least one small page in the huge extent.
  1771				 * Be careful to retry when appropriate, but not forever!
  1772				 * Elsewhere -EEXIST would be the right code, but not here.
  1773				 */
  1774				if (xa_find(&mapping->i_pages, &index,
  1775					index + HPAGE_PMD_NR - 1, XA_PRESENT))
  1776					return ERR_PTR(-E2BIG);
  1777			}
  1778	
  1779			order = highest_order(suitable_orders);
> 1780			while (suitable_orders) {
  1781				pages = 1 << order;
  1782				index = round_down(index, pages);
  1783				folio = shmem_alloc_hugefolio(gfp, info, index, order);
  1784				if (folio)
  1785					goto allocated;
  1786	
  1787				if (pages == HPAGE_PMD_NR)
  1788					count_vm_event(THP_FILE_FALLBACK);
  1789				order = next_order(&suitable_orders, order);
  1790			}
  1791		} else {
  1792			pages = 1;
  1793			folio = shmem_alloc_folio(gfp, info, index);
  1794		}
  1795		if (!folio)
  1796			return ERR_PTR(-ENOMEM);
  1797	
  1798	allocated:
  1799		__folio_set_locked(folio);
  1800		__folio_set_swapbacked(folio);
  1801	
  1802		gfp &= GFP_RECLAIM_MASK;
  1803		error = mem_cgroup_charge(folio, fault_mm, gfp);
  1804		if (error) {
  1805			if (xa_find(&mapping->i_pages, &index,
  1806					index + pages - 1, XA_PRESENT)) {
  1807				error = -EEXIST;
  1808			} else if (pages == HPAGE_PMD_NR) {
  1809				count_vm_event(THP_FILE_FALLBACK);
  1810				count_vm_event(THP_FILE_FALLBACK_CHARGE);
  1811			}
  1812			goto unlock;
  1813		}
  1814	
  1815		error = shmem_add_to_page_cache(folio, mapping, index, NULL, gfp);
  1816		if (error)
  1817			goto unlock;
  1818	
  1819		error = shmem_inode_acct_blocks(inode, pages);
  1820		if (error) {
  1821			struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
  1822			long freed;
  1823			/*
  1824			 * Try to reclaim some space by splitting a few
  1825			 * large folios beyond i_size on the filesystem.
  1826			 */
  1827			shmem_unused_huge_shrink(sbinfo, NULL, 2);
  1828			/*
  1829			 * And do a shmem_recalc_inode() to account for freed pages:
  1830			 * except our folio is there in cache, so not quite balanced.
  1831			 */
  1832			spin_lock(&info->lock);
  1833			freed = pages + info->alloced - info->swapped -
  1834				READ_ONCE(mapping->nrpages);
  1835			if (freed > 0)
  1836				info->alloced -= freed;
  1837			spin_unlock(&info->lock);
  1838			if (freed > 0)
  1839				shmem_inode_unacct_blocks(inode, freed);
  1840			error = shmem_inode_acct_blocks(inode, pages);
  1841			if (error) {
  1842				filemap_remove_folio(folio);
  1843				goto unlock;
  1844			}
  1845		}
  1846	
  1847		shmem_recalc_inode(inode, pages, 0);
  1848		folio_add_lru(folio);
  1849		return folio;
  1850	
  1851	unlock:
  1852		folio_unlock(folio);
  1853		folio_put(folio);
  1854		return ERR_PTR(error);
  1855	}
  1856	

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