ext4: remove page_skipped hackery in ext4_da_writepages() (ee6ecbcc) · Commits · 戴 / test

Because the ext4 page writeback codepath had been prematurely calling clear_page_dirty_for_io(), if it turned out that a particular page couldn't be written out during a particular pass of write_cache_pages_da(), the page would have to get redirtied by calling redirty_pages_for_writeback(). Not only was this wasted work, but redirty_page_for_writeback() would increment wbc->pages_skipped to signal to writeback_sb_inodes() that buffers were locked, and that it should skip this inode until later. Since this signal was incorrect in ext4's case --- which was caused by ext4's historically incorrect use of write_cache_pages() --- ext4_da_writepages() saved and restored wbc->skipped_pages to avoid confusing writeback_sb_inodes(). Now that we've fixed ext4 to call clear_page_dirty_for_io() right before initiating the page I/O, we can nuke the page_skipped save/restore hackery, and breathe a sigh of relief. Signed-off-by:

"Theodore Ts'o" <tytso@mit.edu>

fs/ext4/inode.c

+0 −10

Original line number	Diff line number	Diff line
		@@ -2900,7 +2900,6 @@ static int ext4_da_writepages(struct address_space *mapping,
		struct mpage_da_data mpd;
		struct inode *inode = mapping->host;
		int pages_written = 0;
		long pages_skipped;
		unsigned int max_pages;
		int range_cyclic, cycled = 1, io_done = 0;
		int needed_blocks, ret = 0;
		@@ -2986,8 +2985,6 @@ static int ext4_da_writepages(struct address_space *mapping,
		mpd.wbc = wbc;
		mpd.inode = mapping->host;

		pages_skipped = wbc->pages_skipped;

		retry:
		if (wbc->sync_mode == WB_SYNC_ALL)
		tag_pages_for_writeback(mapping, index, end);
		@@ -3047,7 +3044,6 @@ retry:
		* and try again
		*/
		jbd2_journal_force_commit_nested(sbi->s_journal);
		wbc->pages_skipped = pages_skipped;
		ret = 0;
		} else if (ret == MPAGE_DA_EXTENT_TAIL) {
		/*
		@@ -3055,7 +3051,6 @@ retry:
		* rest of the pages
		*/
		pages_written += mpd.pages_written;
		wbc->pages_skipped = pages_skipped;
		ret = 0;
		io_done = 1;
		} else if (wbc->nr_to_write)
		@@ -3073,11 +3068,6 @@ retry:
		wbc->range_end = mapping->writeback_index - 1;
		goto retry;
		}
		if (pages_skipped != wbc->pages_skipped)
		ext4_msg(inode->i_sb, KERN_CRIT,
		"This should not happen leaving %s "
		"with nr_to_write = %ld ret = %d",
		__func__, wbc->nr_to_write, ret);

		/* Update index */
		wbc->range_cyclic = range_cyclic;

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