Re: [RFC] writeback: add elastic bdi in cgwb bdp

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

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Hi Hillf,

[FYI, it's a private test report for your RFC patch.]
[auto build test ERROR on linus/master]
[cannot apply to v5.4-rc2 next-20191011]
[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/Hillf-Danton/writeback-add-elastic-bdi-in-cgwb-bdp/20191014-014906
config: i386-tinyconfig (attached as .config)
compiler: gcc-7 (Debian 7.4.0-13) 7.4.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

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

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

   mm/page-writeback.c: In function 'balance_dirty_pages_ratelimited':
>> mm/page-writeback.c:1954:4: error: implicit declaration of function 'cgwb_bdp' [-Werror=implicit-function-declaration]
       cgwb_bdp(wb);
       ^~~~~~~~
>> mm/page-writeback.c:1951:5: warning: suggest explicit braces to avoid ambiguous 'else' [-Wdangling-else]
     if (unlikely(current->nr_dirtied >= ratelimit))
        ^
   cc1: some warnings being treated as errors
--
   In file included from mm/backing-dev.c:3:0:
   mm/backing-dev.c: In function 'wb_init':
>> mm/backing-dev.c:329:26: error: 'struct bdi_writeback' has no member named 'bdp_waitq'
      init_waitqueue_head(&wb->bdp_waitq);
                             ^
   include/linux/wait.h:67:26: note: in definition of macro 'init_waitqueue_head'
      __init_waitqueue_head((wq_head), #wq_head, &__key);  \
                             ^~~~~~~

vim +/cgwb_bdp +1954 mm/page-writeback.c

  1889	
  1890	/**
  1891	 * balance_dirty_pages_ratelimited - balance dirty memory state
  1892	 * @mapping: address_space which was dirtied
  1893	 *
  1894	 * Processes which are dirtying memory should call in here once for each page
  1895	 * which was newly dirtied.  The function will periodically check the system's
  1896	 * dirty state and will initiate writeback if needed.
  1897	 *
  1898	 * On really big machines, get_writeback_state is expensive, so try to avoid
  1899	 * calling it too often (ratelimiting).  But once we're over the dirty memory
  1900	 * limit we decrease the ratelimiting by a lot, to prevent individual processes
  1901	 * from overshooting the limit by (ratelimit_pages) each.
  1902	 */
  1903	void balance_dirty_pages_ratelimited(struct address_space *mapping)
  1904	{
  1905		struct inode *inode = mapping->host;
  1906		struct backing_dev_info *bdi = inode_to_bdi(inode);
  1907		struct bdi_writeback *wb = NULL;
  1908		int ratelimit;
  1909		int *p;
  1910	
  1911		if (!bdi_cap_account_dirty(bdi))
  1912			return;
  1913	
  1914		if (inode_cgwb_enabled(inode))
  1915			wb = wb_get_create_current(bdi, GFP_KERNEL);
  1916		if (!wb)
  1917			wb = &bdi->wb;
  1918	
  1919		ratelimit = current->nr_dirtied_pause;
  1920		if (wb->dirty_exceeded)
  1921			ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
  1922	
  1923		preempt_disable();
  1924		/*
  1925		 * This prevents one CPU to accumulate too many dirtied pages without
  1926		 * calling into balance_dirty_pages(), which can happen when there are
  1927		 * 1000+ tasks, all of them start dirtying pages at exactly the same
  1928		 * time, hence all honoured too large initial task->nr_dirtied_pause.
  1929		 */
  1930		p =  this_cpu_ptr(&bdp_ratelimits);
  1931		if (unlikely(current->nr_dirtied >= ratelimit))
  1932			*p = 0;
  1933		else if (unlikely(*p >= ratelimit_pages)) {
  1934			*p = 0;
  1935			ratelimit = 0;
  1936		}
  1937		/*
  1938		 * Pick up the dirtied pages by the exited tasks. This avoids lots of
  1939		 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
  1940		 * the dirty throttling and livelock other long-run dirtiers.
  1941		 */
  1942		p = this_cpu_ptr(&dirty_throttle_leaks);
  1943		if (*p > 0 && current->nr_dirtied < ratelimit) {
  1944			unsigned long nr_pages_dirtied;
  1945			nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
  1946			*p -= nr_pages_dirtied;
  1947			current->nr_dirtied += nr_pages_dirtied;
  1948		}
  1949		preempt_enable();
  1950	
> 1951		if (unlikely(current->nr_dirtied >= ratelimit))
  1952			if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK) &&
  1953			    IS_ENABLED(CONFIG_CGWB_BDP_WITH_EBDI))
> 1954				cgwb_bdp(wb);
  1955			else
  1956				balance_dirty_pages(wb, current->nr_dirtied);
  1957	
  1958		wb_put(wb);
  1959	}
  1960	EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
  1961	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

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