Re: [PATCH 2/2] kpageflags: fix wrong KPF_THP on non-pmd-mappable compound pages

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

Hi ran,

kernel test robot noticed the following build warnings:

[auto build test WARNING on akpm-mm/mm-everything]
[also build test WARNING on linus/master v6.10-rc5 next-20240625]
[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/ran-xiaokai/mm-Constify-folio_order-folio_test_pmd_mappable/20240626-113027
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20240626024924.1155558-3-ranxiaokai627%40163.com
patch subject: [PATCH 2/2] kpageflags: fix wrong KPF_THP on non-pmd-mappable compound pages
config: parisc-allnoconfig (https://download.01.org/0day-ci/archive/20240626/202406262203.FFeFYbhP-lkp@intel.com/config)
compiler: hppa-linux-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240626/202406262203.FFeFYbhP-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/202406262203.FFeFYbhP-lkp@intel.com/

All warnings (new ones prefixed by >>):

   fs/proc/page.c: In function 'stable_page_flags':
>> fs/proc/page.c:151:42: warning: passing argument 1 of 'folio_test_pmd_mappable' discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
     151 |         else if (folio_test_pmd_mappable(folio)) {
         |                                          ^~~~~
   In file included from include/linux/mm.h:1120,
                    from include/linux/memblock.h:12,
                    from fs/proc/page.c:2:
   include/linux/huge_mm.h:438:58: note: expected 'struct folio *' but argument is of type 'const struct folio *'
     438 | static inline bool folio_test_pmd_mappable(struct folio *folio)
         |                                            ~~~~~~~~~~~~~~^~~~~


vim +151 fs/proc/page.c

   108	
   109	u64 stable_page_flags(const struct page *page)
   110	{
   111		const struct folio *folio;
   112		unsigned long k;
   113		unsigned long mapping;
   114		bool is_anon;
   115		u64 u = 0;
   116	
   117		/*
   118		 * pseudo flag: KPF_NOPAGE
   119		 * it differentiates a memory hole from a page with no flags
   120		 */
   121		if (!page)
   122			return 1 << KPF_NOPAGE;
   123		folio = page_folio(page);
   124	
   125		k = folio->flags;
   126		mapping = (unsigned long)folio->mapping;
   127		is_anon = mapping & PAGE_MAPPING_ANON;
   128	
   129		/*
   130		 * pseudo flags for the well known (anonymous) memory mapped pages
   131		 */
   132		if (page_mapped(page))
   133			u |= 1 << KPF_MMAP;
   134		if (is_anon) {
   135			u |= 1 << KPF_ANON;
   136			if (mapping & PAGE_MAPPING_KSM)
   137				u |= 1 << KPF_KSM;
   138		}
   139	
   140		/*
   141		 * compound pages: export both head/tail info
   142		 * they together define a compound page's start/end pos and order
   143		 */
   144		if (page == &folio->page)
   145			u |= kpf_copy_bit(k, KPF_COMPOUND_HEAD, PG_head);
   146		else
   147			u |= 1 << KPF_COMPOUND_TAIL;
   148	
   149		if (folio_test_hugetlb(folio))
   150			u |= 1 << KPF_HUGE;
 > 151		else if (folio_test_pmd_mappable(folio)) {
   152			u |= 1 << KPF_THP;
   153			if (is_huge_zero_folio(folio))
   154				u |= 1 << KPF_ZERO_PAGE;
   155		} else if (is_zero_pfn(page_to_pfn(page)))
   156			u |= 1 << KPF_ZERO_PAGE;
   157	
   158		/*
   159		 * Caveats on high order pages: PG_buddy and PG_slab will only be set
   160		 * on the head page.
   161		 */
   162		if (PageBuddy(page))
   163			u |= 1 << KPF_BUDDY;
   164		else if (page_count(page) == 0 && is_free_buddy_page(page))
   165			u |= 1 << KPF_BUDDY;
   166	
   167		if (PageOffline(page))
   168			u |= 1 << KPF_OFFLINE;
   169		if (PageTable(page))
   170			u |= 1 << KPF_PGTABLE;
   171		if (folio_test_slab(folio))
   172			u |= 1 << KPF_SLAB;
   173	

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