Hi,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on linus/master]
[also build test ERROR on next-20221013]
[cannot apply to shuah-kselftest/next v6.0]
[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/alexlzhu-fb-com/THP-Shrinker/20221013-065303
config: i386-randconfig-a004-20220822
compiler: gcc-11 (Debian 11.3.0-5) 11.3.0
reproduce (this is a W=1 build):
        # https://github.com/intel-lab-lkp/linux/commit/ae565d00fb30b75b8c92e327aa3b25211950a0ff
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review alexlzhu-fb-com/THP-Shrinker/20221013-065303
        git checkout ae565d00fb30b75b8c92e327aa3b25211950a0ff
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   mm/migrate.c: In function 'try_to_unmap_clean':
>> mm/migrate.c:205:32: error: 'THP_SPLIT_REMAP_READONLY_ZERO_PAGE' undeclared (first use in this function)
     205 |                 count_vm_event(THP_SPLIT_REMAP_READONLY_ZERO_PAGE);
         |                                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   mm/migrate.c:205:32: note: each undeclared identifier is reported only once for each function it appears in
>> mm/migrate.c:210:24: error: 'THP_SPLIT_UNMAP' undeclared (first use in this function)
     210 |         count_vm_event(THP_SPLIT_UNMAP);
         |                        ^~~~~~~~~~~~~~~


vim +/THP_SPLIT_REMAP_READONLY_ZERO_PAGE +205 mm/migrate.c

   170	
   171	static bool try_to_unmap_clean(struct page_vma_mapped_walk *pvmw, struct page *page)
   172	{
   173		void *addr;
   174		bool dirty;
   175		pte_t newpte;
   176	
   177		VM_BUG_ON_PAGE(PageCompound(page), page);
   178		VM_BUG_ON_PAGE(!PageAnon(page), page);
   179		VM_BUG_ON_PAGE(!PageLocked(page), page);
   180		VM_BUG_ON_PAGE(pte_present(*pvmw->pte), page);
   181	
   182		if (PageMlocked(page) || (pvmw->vma->vm_flags & VM_LOCKED))
   183			return false;
   184	
   185		/*
   186		 * The pmd entry mapping the old thp was flushed and the pte mapping
   187		 * this subpage has been non present. Therefore, this subpage is
   188		 * inaccessible. We don't need to remap it if it contains only zeros.
   189		 */
   190		addr = kmap_local_page(page);
   191		dirty = memchr_inv(addr, 0, PAGE_SIZE);
   192		kunmap_local(addr);
   193	
   194		if (dirty)
   195			return false;
   196	
   197		pte_clear_not_present_full(pvmw->vma->vm_mm, pvmw->address, pvmw->pte, false);
   198	
   199		if (userfaultfd_armed(pvmw->vma)) {
   200			newpte = pte_mkspecial(pfn_pte(page_to_pfn(ZERO_PAGE(pvmw->address)),
   201						       pvmw->vma->vm_page_prot));
   202			ptep_clear_flush(pvmw->vma, pvmw->address, pvmw->pte);
   203			set_pte_at(pvmw->vma->vm_mm, pvmw->address, pvmw->pte, newpte);
   204			dec_mm_counter(pvmw->vma->vm_mm, MM_ANONPAGES);
 > 205			count_vm_event(THP_SPLIT_REMAP_READONLY_ZERO_PAGE);
   206			return true;
   207		}
   208	
   209		dec_mm_counter(pvmw->vma->vm_mm, mm_counter(page));
 > 210		count_vm_event(THP_SPLIT_UNMAP);
   211		return true;
   212	}
   213	

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