Commit 9a01b56b authored Sep 07, 2014 by Huang Ying Committed by Jaegeuk Kim Sep 09, 2014

f2fs: avoid node page to be written twice in gc_node_segment



In gc_node_segment, if node page gc is run concurrently with node page
writeback, and check_valid_map and get_node_page run after page locked
and before cur_valid_map is updated as below, it is possible for the
page to be written twice unnecessarily.

			sync_node_pages
			  try_lock_page
			  ...
check_valid_map		  f2fs_write_node_page
			    ...
			    write_node_page
			      do_write_page
			        allocate_data_block
				  ...
				  refresh_sit_entry /* update cur_valid_map */
				  ...
			    ...
			    unlock_page
get_node_page
...
set_page_dirty
...
f2fs_put_page
  unlock_page

This can be solved via calling check_valid_map after get_node_page again.

Signed-off-by: Huang, Ying <ying.huang@intel.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

parent 721bd4d5

fs/f2fs/gc.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -423,6 +423,12 @@ next_step:
		if (IS_ERR(node_page))
		continue;

		/* block may become invalid during get_node_page */
		if (check_valid_map(sbi, segno, off) == 0) {
		f2fs_put_page(node_page, 1);
		continue;
		}

		/* set page dirty and write it */
		if (gc_type == FG_GC) {
		f2fs_wait_on_page_writeback(node_page, NODE);

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