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: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index d1906d9..7e91913e 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2282,13 +2282,12 @@
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 @@
*/
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 @@
}
out_writepages:
- wbc->nr_to_write = to_write;
+ wbc->nr_to_write = to_write - nr_to_writebump;
wbc->range_start = range_start;
return ret;
}
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 865e9dd..e0e3a5e 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -3282,6 +3282,35 @@
}
/*
+ * 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
*/
static noinline_for_stack int
@@ -3290,7 +3319,8 @@
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 @@
/* 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 @@
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;
}
