Hi John,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on linus/master]
[also build test ERROR on v4.18-rc3]
[cannot apply to next-20180629]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/john-hubbard-gmail-com/mm-fs-gup-don-t-unmap-or-drop-filesystem-buffers/20180702-090125
config: i386-randconfig-x074-201826 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-16) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All error/warnings (new ones prefixed by >>):

   In file included from include/asm-generic/atomic-instrumented.h:16:0,
                    from arch/x86/include/asm/atomic.h:283,
                    from include/linux/atomic.h:5,
                    from include/linux/page_counter.h:5,
                    from mm/memcontrol.c:34:
   mm/memcontrol.c: In function 'unlock_page_lru':
>> mm/memcontrol.c:2087:32: error: 'page_tail' undeclared (first use in this function); did you mean 'page_pool'?
      VM_BUG_ON_PAGE(PageDmaPinned(page_tail), page);
                                   ^
   include/linux/build_bug.h:36:63: note: in definition of macro 'BUILD_BUG_ON_INVALID'
    #define BUILD_BUG_ON_INVALID(e) ((void)(sizeof((__force long)(e))))
                                                                  ^
>> include/linux/mmdebug.h:46:36: note: in expansion of macro 'VM_BUG_ON'
    #define VM_BUG_ON_PAGE(cond, page) VM_BUG_ON(cond)
                                       ^~~~~~~~~
>> mm/memcontrol.c:2087:3: note: in expansion of macro 'VM_BUG_ON_PAGE'
      VM_BUG_ON_PAGE(PageDmaPinned(page_tail), page);
      ^~~~~~~~~~~~~~
   mm/memcontrol.c:2087:32: note: each undeclared identifier is reported only once for each function it appears in
      VM_BUG_ON_PAGE(PageDmaPinned(page_tail), page);
                                   ^
   include/linux/build_bug.h:36:63: note: in definition of macro 'BUILD_BUG_ON_INVALID'
    #define BUILD_BUG_ON_INVALID(e) ((void)(sizeof((__force long)(e))))
                                                                  ^
>> include/linux/mmdebug.h:46:36: note: in expansion of macro 'VM_BUG_ON'
    #define VM_BUG_ON_PAGE(cond, page) VM_BUG_ON(cond)
                                       ^~~~~~~~~
>> mm/memcontrol.c:2087:3: note: in expansion of macro 'VM_BUG_ON_PAGE'
      VM_BUG_ON_PAGE(PageDmaPinned(page_tail), page);
      ^~~~~~~~~~~~~~

vim +2087 mm/memcontrol.c

  2077	
  2078	static void unlock_page_lru(struct page *page, int isolated)
  2079	{
  2080		struct zone *zone = page_zone(page);
  2081	
  2082		if (isolated) {
  2083			struct lruvec *lruvec;
  2084	
  2085			lruvec = mem_cgroup_page_lruvec(page, zone->zone_pgdat);
  2086			VM_BUG_ON_PAGE(PageLRU(page), page);
> 2087			VM_BUG_ON_PAGE(PageDmaPinned(page_tail), page);
  2088	
  2089			SetPageLRU(page);
  2090			add_page_to_lru_list(page, lruvec, page_lru(page));
  2091		}
  2092		spin_unlock_irq(zone_lru_lock(zone));
  2093	}
  2094	

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