Hi Aleksei,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on linus/master]
[also build test ERROR on v4.17-rc2 next-20180424]
[cannot apply to dgc-xfs/for-next]
[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/Aleksei-Besogonov/fs-Add-iomap_swap_activate/20180423-061348
config: x86_64-randconfig-s2-04260250 (attached as .config)
compiler: gcc-6 (Debian 6.4.0-9) 6.4.0 20171026
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All errors (new ones prefixed by >>):

   fs/iomap.c: In function 'iomap_swap_map':
>> fs/iomap.c:1130:8: error: implicit declaration of function 'add_swap_extent' [-Werror=implicit-function-declaration]
     ret = add_swap_extent(ctx->sis, ctx->page_no, num_pages, disk_pos);
           ^~~~~~~~~~~~~~~
   cc1: some warnings being treated as errors

vim +/add_swap_extent +1130 fs/iomap.c

  1100	
  1101	static loff_t
  1102	iomap_swap_map(struct inode *inode, loff_t pos, loff_t length,
  1103			void *data, struct iomap *iomap)
  1104	{
  1105		struct iomap_swap_walker_context *ctx = data;
  1106		unsigned int blocks_per_page = PAGE_SIZE >> inode->i_blkbits;
  1107		u64 num_pages;
  1108		u64 aligned_address;
  1109		sector_t disk_pos;
  1110		loff_t eff_length;
  1111		loff_t ret;
  1112	
  1113		/*
  1114		 * Swap extents need to be PAGE_SIZE aligned on the disk
  1115		 */
  1116		aligned_address = ALIGN(iomap->addr, PAGE_SIZE);
  1117		eff_length = length - (aligned_address - iomap->addr);
  1118		BUG_ON(eff_length > length);
  1119		disk_pos = aligned_address >> inode->i_blkbits;
  1120	
  1121		if (eff_length < 0)
  1122			return length; /* Continue probing */
  1123	
  1124		num_pages = eff_length / PAGE_SIZE;
  1125	
  1126		/* Can't add blocks less than 1 page */
  1127		if (num_pages == 0)
  1128			return length; /* Continue probing */
  1129	
> 1130		ret = add_swap_extent(ctx->sis, ctx->page_no, num_pages, disk_pos);
  1131		if (ret < 0)
  1132			return ret;
  1133	
  1134		ctx->nr_extents += ret;
  1135		ctx->page_no += num_pages;
  1136		*(ctx->span) += num_pages * blocks_per_page;
  1137	
  1138		return length; /* continue probing */
  1139	}
  1140	

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