Re: [PATCH] vfs: keep inodes with page cache off the inode shrinker LRU

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

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Hi Johannes,

I love your patch! Yet something to improve:

[auto build test ERROR on vfs/for-next]
[also build test ERROR on linux/master linus/master v5.6-rc1 next-20200213]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Johannes-Weiner/vfs-keep-inodes-with-page-cache-off-the-inode-shrinker-LRU/20200214-083756
base:   https://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git for-next
config: m68k-allmodconfig (attached as .config)
compiler: m68k-linux-gcc (GCC) 7.5.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=7.5.0 make.cross ARCH=m68k 

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

All errors (new ones prefixed by >>):

   fs/dax.c: In function 'grab_mapping_entry':
>> fs/dax.c:556:28: error: 'struct address_space' has no member named 'inode'
      inode_pages_clear(mapping->inode);
                               ^~
   fs/dax.c:558:26: error: 'struct address_space' has no member named 'inode'
      inode_pages_set(mapping->inode);
                             ^~

vim +556 fs/dax.c

   446	
   447	/*
   448	 * Find page cache entry at given index. If it is a DAX entry, return it
   449	 * with the entry locked. If the page cache doesn't contain an entry at
   450	 * that index, add a locked empty entry.
   451	 *
   452	 * When requesting an entry with size DAX_PMD, grab_mapping_entry() will
   453	 * either return that locked entry or will return VM_FAULT_FALLBACK.
   454	 * This will happen if there are any PTE entries within the PMD range
   455	 * that we are requesting.
   456	 *
   457	 * We always favor PTE entries over PMD entries. There isn't a flow where we
   458	 * evict PTE entries in order to 'upgrade' them to a PMD entry.  A PMD
   459	 * insertion will fail if it finds any PTE entries already in the tree, and a
   460	 * PTE insertion will cause an existing PMD entry to be unmapped and
   461	 * downgraded to PTE entries.  This happens for both PMD zero pages as
   462	 * well as PMD empty entries.
   463	 *
   464	 * The exception to this downgrade path is for PMD entries that have
   465	 * real storage backing them.  We will leave these real PMD entries in
   466	 * the tree, and PTE writes will simply dirty the entire PMD entry.
   467	 *
   468	 * Note: Unlike filemap_fault() we don't honor FAULT_FLAG_RETRY flags. For
   469	 * persistent memory the benefit is doubtful. We can add that later if we can
   470	 * show it helps.
   471	 *
   472	 * On error, this function does not return an ERR_PTR.  Instead it returns
   473	 * a VM_FAULT code, encoded as an xarray internal entry.  The ERR_PTR values
   474	 * overlap with xarray value entries.
   475	 */
   476	static void *grab_mapping_entry(struct xa_state *xas,
   477			struct address_space *mapping, unsigned int order)
   478	{
   479		unsigned long index = xas->xa_index;
   480		bool pmd_downgrade = false; /* splitting PMD entry into PTE entries? */
   481		int populated;
   482		void *entry;
   483	
   484	retry:
   485		populated = 0;
   486		xas_lock_irq(xas);
   487		entry = get_unlocked_entry(xas, order);
   488	
   489		if (entry) {
   490			if (dax_is_conflict(entry))
   491				goto fallback;
   492			if (!xa_is_value(entry)) {
   493				xas_set_err(xas, EIO);
   494				goto out_unlock;
   495			}
   496	
   497			if (order == 0) {
   498				if (dax_is_pmd_entry(entry) &&
   499				    (dax_is_zero_entry(entry) ||
   500				     dax_is_empty_entry(entry))) {
   501					pmd_downgrade = true;
   502				}
   503			}
   504		}
   505	
   506		if (pmd_downgrade) {
   507			/*
   508			 * Make sure 'entry' remains valid while we drop
   509			 * the i_pages lock.
   510			 */
   511			dax_lock_entry(xas, entry);
   512	
   513			/*
   514			 * Besides huge zero pages the only other thing that gets
   515			 * downgraded are empty entries which don't need to be
   516			 * unmapped.
   517			 */
   518			if (dax_is_zero_entry(entry)) {
   519				xas_unlock_irq(xas);
   520				unmap_mapping_pages(mapping,
   521						xas->xa_index & ~PG_PMD_COLOUR,
   522						PG_PMD_NR, false);
   523				xas_reset(xas);
   524				xas_lock_irq(xas);
   525			}
   526	
   527			dax_disassociate_entry(entry, mapping, false);
   528			xas_store(xas, NULL);	/* undo the PMD join */
   529			dax_wake_entry(xas, entry, true);
   530			mapping->nrexceptional--;
   531			if (mapping_empty(mapping))
   532				populated = -1;
   533			entry = NULL;
   534			xas_set(xas, index);
   535		}
   536	
   537		if (entry) {
   538			dax_lock_entry(xas, entry);
   539		} else {
   540			unsigned long flags = DAX_EMPTY;
   541	
   542			if (order > 0)
   543				flags |= DAX_PMD;
   544			entry = dax_make_entry(pfn_to_pfn_t(0), flags);
   545			dax_lock_entry(xas, entry);
   546			if (xas_error(xas))
   547				goto out_unlock;
   548			if (mapping_empty(mapping))
   549				populated++;
   550			mapping->nrexceptional++;
   551		}
   552	
   553	out_unlock:
   554		xas_unlock_irq(xas);
   555		if (populated == -1)
 > 556			inode_pages_clear(mapping->inode);
   557		else if (populated == 1)
   558			inode_pages_set(mapping->inode);
   559		if (xas_nomem(xas, mapping_gfp_mask(mapping) & ~__GFP_HIGHMEM))
   560			goto retry;
   561		if (xas->xa_node == XA_ERROR(-ENOMEM))
   562			return xa_mk_internal(VM_FAULT_OOM);
   563		if (xas_error(xas))
   564			return xa_mk_internal(VM_FAULT_SIGBUS);
   565		return entry;
   566	fallback:
   567		xas_unlock_irq(xas);
   568		return xa_mk_internal(VM_FAULT_FALLBACK);
   569	}
   570	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

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