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Commit 22208ded authored by Aneesh Kumar K.V's avatar Aneesh Kumar K.V Committed by Theodore Ts'o
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ext4: Fix file fragmentation during large file write. 



The range_cyclic writeback mode uses the address_space writeback_index
as the start index for writeback.  With delayed allocation we were
updating writeback_index wrongly resulting in highly fragmented file.
This patch reduces the number of extents reduced from 4000 to 27 for a
3GB file.

Signed-off-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 17bc6c30

fs/ext4/inode.c

+57 −34
Original line number Diff line number Diff line
@@ -1648,6 +1648,7 @@ static int mpage_da_submit_io(struct mpage_da_data *mpd) 
	int ret = 0, err, nr_pages, i;

	unsigned long index, end;

	struct pagevec pvec;

	long pages_skipped;



	BUG_ON(mpd->next_page <= mpd->first_page);

	pagevec_init(&pvec, 0);
@@ -1655,7 +1656,6 @@ static int mpage_da_submit_io(struct mpage_da_data *mpd) 
	end = mpd->next_page - 1;



	while (index <= end) {

		/* XXX: optimize tail */

		/*

		 * We can use PAGECACHE_TAG_DIRTY lookup here because

		 * even though we have cleared the dirty flag on the page
@@ -1673,8 +1673,13 @@ static int mpage_da_submit_io(struct mpage_da_data *mpd) 
		for (i = 0; i < nr_pages; i++) {

			struct page *page = pvec.pages[i];



			pages_skipped = mpd->wbc->pages_skipped;

			err = mapping->a_ops->writepage(page, mpd->wbc);

			if (!err)

			if (!err && (pages_skipped == mpd->wbc->pages_skipped))

				/*

				 * have successfully written the page

				 * without skipping the same

				 */

				mpd->pages_written++;

			/*

			 * In error case, we have to continue because
@@ -2110,7 +2115,6 @@ static int mpage_da_writepages(struct address_space *mapping, 
			       struct writeback_control *wbc,

			       struct mpage_da_data *mpd)

{

	long to_write;

	int ret;



	if (!mpd->get_block)
@@ -2125,19 +2129,18 @@ static int mpage_da_writepages(struct address_space *mapping, 
	mpd->pages_written = 0;

	mpd->retval = 0;



	to_write = wbc->nr_to_write;



	ret = write_cache_pages(mapping, wbc, __mpage_da_writepage, mpd);



	/*

	 * Handle last extent of pages

	 */

	if (!mpd->io_done && mpd->next_page != mpd->first_page) {

		if (mpage_da_map_blocks(mpd) == 0)

			mpage_da_submit_io(mpd);

	}



	wbc->nr_to_write = to_write - mpd->pages_written;

		mpd->io_done = 1;

		ret = MPAGE_DA_EXTENT_TAIL;

	}

	wbc->nr_to_write -= mpd->pages_written;

	return ret;

}
@@ -2366,11 +2369,14 @@ static int ext4_da_writepages_trans_blocks(struct inode *inode) 
static int ext4_da_writepages(struct address_space *mapping,

			      struct writeback_control *wbc)

{

	pgoff_t	index;

	int range_whole = 0;

	handle_t *handle = NULL;

	struct mpage_da_data mpd;

	struct inode *inode = mapping->host;

	int no_nrwrite_index_update;

	long pages_written = 0, pages_skipped;

	int needed_blocks, ret = 0, nr_to_writebump = 0;

	long to_write, pages_skipped = 0;

	struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb);



	/*
@@ -2390,16 +2396,26 @@ static int ext4_da_writepages(struct address_space *mapping, 
		nr_to_writebump = sbi->s_mb_stream_request - wbc->nr_to_write;

		wbc->nr_to_write = sbi->s_mb_stream_request;

	}

	if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)

		range_whole = 1;





	pages_skipped = wbc->pages_skipped;

	if (wbc->range_cyclic)

		index = mapping->writeback_index;

	else

		index = wbc->range_start >> PAGE_CACHE_SHIFT;



	mpd.wbc = wbc;

	mpd.inode = mapping->host;



restart_loop:

	to_write = wbc->nr_to_write;

	while (!ret && to_write > 0) {

	/*

	 * we don't want write_cache_pages to update

	 * nr_to_write and writeback_index

	 */

	no_nrwrite_index_update = wbc->no_nrwrite_index_update;

	wbc->no_nrwrite_index_update = 1;

	pages_skipped = wbc->pages_skipped;



	while (!ret && wbc->nr_to_write > 0) {



		/*

		 * we  insert one extent at a time. So we need
@@ -2420,46 +2436,53 @@ static int ext4_da_writepages(struct address_space *mapping, 
			dump_stack();

			goto out_writepages;

		}

		to_write -= wbc->nr_to_write;



		mpd.get_block = ext4_da_get_block_write;

		ret = mpage_da_writepages(mapping, wbc, &mpd);



		ext4_journal_stop(handle);



		if (mpd.retval == -ENOSPC)

		if (mpd.retval == -ENOSPC) {

			/* commit the transaction which would

			 * free blocks released in the transaction

			 * and try again

			 */

			jbd2_journal_force_commit_nested(sbi->s_journal);



		/* reset the retry count */

		if (ret == MPAGE_DA_EXTENT_TAIL) {

			wbc->pages_skipped = pages_skipped;

			ret = 0;

		} else if (ret == MPAGE_DA_EXTENT_TAIL) {

			/*

			 * got one extent now try with

			 * rest of the pages

			 */

			to_write += wbc->nr_to_write;

			pages_written += mpd.pages_written;

			wbc->pages_skipped = pages_skipped;

			ret = 0;

		} else if (wbc->nr_to_write) {

		} else if (wbc->nr_to_write)

			/*

			 * There is no more writeout needed

			 * or we requested for a noblocking writeout

			 * and we found the device congested

			 */

			to_write += wbc->nr_to_write;

			break;

	}

		wbc->nr_to_write = to_write;

	}

	if (pages_skipped != wbc->pages_skipped)

		printk(KERN_EMERG "This should not happen leaving %s "

				"with nr_to_write = %ld ret = %d\n",

				__func__, wbc->nr_to_write, ret);



	if (!wbc->range_cyclic && (pages_skipped != wbc->pages_skipped)) {

		/* We skipped pages in this loop */

		wbc->nr_to_write = to_write +

				wbc->pages_skipped - pages_skipped;

		wbc->pages_skipped = pages_skipped;

		goto restart_loop;

	}

	/* Update index */

	index += pages_written;

	if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))

		/*

		 * set the writeback_index so that range_cyclic

		 * mode will write it back later

		 */

		mapping->writeback_index = index;



out_writepages:

	wbc->nr_to_write = to_write - nr_to_writebump;

	if (!no_nrwrite_index_update)

		wbc->no_nrwrite_index_update = 0;

	wbc->nr_to_write -= nr_to_writebump;

	return ret;

}