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Commit 5e745b04 authored by Aneesh Kumar K.V's avatar Aneesh Kumar K.V Committed by Theodore Ts'o
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ext4: Fix small file fragmentation 



For small file block allocations, mballoc uses per cpu prealloc
space.  Use goal block when searching for the right prealloc
space.  Also make sure ext4_da_writepages tries to write
all the pages for small files in single attempt

Signed-off-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent 91246c00

fs/ext4/inode.c

+15 −6
Original line number Diff line number Diff line
@@ -2282,13 +2282,12 @@ static int ext4_da_writepages_trans_blocks(struct inode *inode) 
static int ext4_da_writepages(struct address_space *mapping,

			      struct writeback_control *wbc)

{

	struct inode *inode = mapping->host;

	handle_t *handle = NULL;

	int needed_blocks;

	int ret = 0;

	long to_write;

	loff_t range_start = 0;

	long pages_skipped = 0;

	struct inode *inode = mapping->host;

	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);



	/*

	 * No pages to write? This is mainly a kludge to avoid starting
@@ -2297,6 +2296,16 @@ static int ext4_da_writepages(struct address_space *mapping, 
	 */

	if (!mapping->nrpages || !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))

		return 0;

	/*

	 * Make sure nr_to_write is >= sbi->s_mb_stream_request

	 * This make sure small files blocks are allocated in

	 * single attempt. This ensure that small files

	 * get less fragmented.

	 */

	if (wbc->nr_to_write < sbi->s_mb_stream_request) {

		nr_to_writebump = sbi->s_mb_stream_request - wbc->nr_to_write;

		wbc->nr_to_write = sbi->s_mb_stream_request;

	}



	if (!wbc->range_cyclic)

		/*
@@ -2377,7 +2386,7 @@ static int ext4_da_writepages(struct address_space *mapping, 
	}



out_writepages:

	wbc->nr_to_write = to_write;

	wbc->nr_to_write = to_write - nr_to_writebump;

	wbc->range_start = range_start;

	return ret;

}

fs/ext4/mballoc.c

+46 −7
Original line number Diff line number Diff line
@@ -3281,6 +3281,35 @@ static void ext4_mb_use_group_pa(struct ext4_allocation_context *ac, 
	mb_debug("use %u/%u from group pa %p\n", pa->pa_lstart-len, len, pa);

}



/*

 * Return the prealloc space that have minimal distance

 * from the goal block. @cpa is the prealloc

 * space that is having currently known minimal distance

 * from the goal block.

 */

static struct ext4_prealloc_space *

ext4_mb_check_group_pa(ext4_fsblk_t goal_block,

			struct ext4_prealloc_space *pa,

			struct ext4_prealloc_space *cpa)

{

	ext4_fsblk_t cur_distance, new_distance;



	if (cpa == NULL) {

		atomic_inc(&pa->pa_count);

		return pa;

	}

	cur_distance = abs(goal_block - cpa->pa_pstart);

	new_distance = abs(goal_block - pa->pa_pstart);



	if (cur_distance < new_distance)

		return cpa;



	/* drop the previous reference */

	atomic_dec(&cpa->pa_count);

	atomic_inc(&pa->pa_count);

	return pa;

}



/*

 * search goal blocks in preallocated space

 */
@@ -3290,7 +3319,8 @@ ext4_mb_use_preallocated(struct ext4_allocation_context *ac) 
	int order, i;

	struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);

	struct ext4_locality_group *lg;

	struct ext4_prealloc_space *pa;

	struct ext4_prealloc_space *pa, *cpa = NULL;

	ext4_fsblk_t goal_block;



	/* only data can be preallocated */

	if (!(ac->ac_flags & EXT4_MB_HINT_DATA))
@@ -3333,6 +3363,13 @@ ext4_mb_use_preallocated(struct ext4_allocation_context *ac) 
		/* The max size of hash table is PREALLOC_TB_SIZE */

		order = PREALLOC_TB_SIZE - 1;



	goal_block = ac->ac_g_ex.fe_group * EXT4_BLOCKS_PER_GROUP(ac->ac_sb) +

		     ac->ac_g_ex.fe_start +

		     le32_to_cpu(EXT4_SB(ac->ac_sb)->s_es->s_first_data_block);

	/*

	 * search for the prealloc space that is having

	 * minimal distance from the goal block.

	 */

	for (i = order; i < PREALLOC_TB_SIZE; i++) {

		rcu_read_lock();

		list_for_each_entry_rcu(pa, &lg->lg_prealloc_list[i],
@@ -3340,17 +3377,19 @@ ext4_mb_use_preallocated(struct ext4_allocation_context *ac) 
			spin_lock(&pa->pa_lock);

			if (pa->pa_deleted == 0 &&

					pa->pa_free >= ac->ac_o_ex.fe_len) {

				atomic_inc(&pa->pa_count);

				ext4_mb_use_group_pa(ac, pa);

				spin_unlock(&pa->pa_lock);

				ac->ac_criteria = 20;

				rcu_read_unlock();

				return 1;



				cpa = ext4_mb_check_group_pa(goal_block,

								pa, cpa);

			}

			spin_unlock(&pa->pa_lock);

		}

		rcu_read_unlock();

	}

	if (cpa) {

		ext4_mb_use_group_pa(ac, cpa);

		ac->ac_criteria = 20;

		return 1;

	}

	return 0;

}