Re: [PATCH 4/4] ext4: Fix file fragmentation during large file write.

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



"Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> writes:

> 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.
> Number of extents reduced from 4000 to 27 for a 3GB file with the below
> patch.
Hi i've played with fragmentation patches with following result:
I've had several crash and deadlocks
for example objects wasn't freed on umount:
 EXT4-fs: mballoc: 12800 blocks 13 reqs (6 success)
 EXT4-fs: mballoc: 7 extents scanned, 12 goal hits, 1 2^N hits, 0 breaks, 0 lost
 EXT4-fs: mballoc: 1 generated and it took 3024
 EXT4-fs: mballoc: 7608 preallocated, 1536 discarded
 slab error in kmem_cache_destroy(): cache `ext4_prealloc_space': Can't free all objects
 Pid: 7703, comm: rmmod Not tainted 2.6.27-rc8 #3
 
 Call Trace:
  [<ffffffff8028b011>] kmem_cache_destroy+0x7d/0xc0
  [<ffffffffa03ca057>] exit_ext4_mballoc+0x10/0x1e [ext4dev]
  [<ffffffffa03d35b3>] exit_ext4_fs+0x1f/0x2f [ext4dev]
  [<ffffffff80250dff>] sys_delete_module+0x199/0x1f3
  [<ffffffff8025d06e>] audit_syscall_entry+0x12d/0x160
  [<ffffffff8020be0b>] system_call_fastpath+0x16/0x1b
Some times sync has stuck.
I'm not shure is it because of current patch set, but where is at least one
brand new bug. See later.
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
> ---
>  fs/ext4/inode.c |   83 +++++++++++++++++++++++++++++++++----------------------
>  1 files changed, 50 insertions(+), 33 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index cba7960..844c136 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -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;
[1] In fact mpd->next_page may be bigger whan (index + wbc->nr_to_write)
this result in incorrect math while exit from mpage_da_writepages()
Probably we have bound end_index here. 
       end = min(mpd->next_page, index +wbc->nr_to_write) -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)
> @@ -2125,10 +2129,7 @@ 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
>  	 */
> @@ -2137,7 +2138,7 @@ static int mpage_da_writepages(struct address_space *mapping,
>  			mpage_da_submit_io(mpd);
>  	}
>  
> -	wbc->nr_to_write = to_write - mpd->pages_written;
> +	wbc->nr_to_write -= mpd->pages_written;
due to [1] wbc->nr_write becomes negative here
>  	return ret;
>  }
>  
> @@ -2366,11 +2367,14 @@ 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;
> +	long pages_written = 0;
>  	struct mpage_da_data mpd;
>  	struct inode *inode = mapping->host;
> +	int no_nrwrite_update, no_index_update;
>  	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 +2394,27 @@ 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_update = wbc->no_nrwrite_update;
> +	wbc->no_nrwrite_update = 1;
> +	no_index_update = wbc->no_index_update;
> +	wbc->no_index_update   = 1;
> +
> +	while (!ret && wbc->nr_to_write > 0) {
>  
>  		/*
>  		 * we  insert one extent at a time. So we need
> @@ -2420,46 +2435,48 @@ 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) {
> +			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;
>  			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 (!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_update)
> +		wbc->no_nrwrite_update = 0;
> +	if (!no_index_update)
> +		wbc->no_index_update   = 0;
> +	wbc->nr_to_write -= nr_to_writebump;
>  	return ret;
>  }
BTW: please add following cleanup fix.
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 6efa4ca..c248cbc 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2603,7 +2603,7 @@ static int ext4_da_write_end(struct file *file,
 	handle_t *handle = ext4_journal_current_handle();
 	loff_t new_i_size;
 	unsigned long start, end;
-	int write_mode = (int)fsdata;
+	int write_mode = (int)(unsigned long)fsdata;
 
 	if (write_mode == FALL_BACK_TO_NONDELALLOC) {
 		if (ext4_should_order_data(inode)) {

--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html

[Index of Archives]     [Reiser Filesystem Development]     [Ceph FS]     [Kernel Newbies]     [Security]     [Netfilter]     [Bugtraq]     [Linux FS]     [Yosemite National Park]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Samba]     [Device Mapper]     [Linux Media]

  Powered by Linux