ext4: Don't allow lg prealloc list to be grow large.
Currently, the locality group prealloc list is freed only when there
is a block allocation failure. This can result in large number of
entries in the preallocation list making ext4_mb_use_preallocated()
expensive.
To fix this, we convert the locality group prealloc list to a hash
list. The hash index is the order of number of blocks in the prealloc
space with a max order of 9. When adding prealloc space to the list we
make sure total entries for each order does not exceed 8. If it is
more than 8 we discard few entries and make sure the we have only <= 5
entries.
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/mballoc.c b/fs/ext4/mballoc.c
index 49bec84..865e9dd 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2480,7 +2480,7 @@
int ext4_mb_init(struct super_block *sb, int needs_recovery)
{
struct ext4_sb_info *sbi = EXT4_SB(sb);
- unsigned i;
+ unsigned i, j;
unsigned offset;
unsigned max;
int ret;
@@ -2552,7 +2552,8 @@
struct ext4_locality_group *lg;
lg = &sbi->s_locality_groups[i];
mutex_init(&lg->lg_mutex);
- INIT_LIST_HEAD(&lg->lg_prealloc_list);
+ for (j = 0; j < PREALLOC_TB_SIZE; j++)
+ INIT_LIST_HEAD(&lg->lg_prealloc_list[j]);
spin_lock_init(&lg->lg_prealloc_lock);
}
@@ -3263,6 +3264,7 @@
struct ext4_prealloc_space *pa)
{
unsigned int len = ac->ac_o_ex.fe_len;
+
ext4_get_group_no_and_offset(ac->ac_sb, pa->pa_pstart,
&ac->ac_b_ex.fe_group,
&ac->ac_b_ex.fe_start);
@@ -3285,6 +3287,7 @@
static noinline_for_stack int
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;
@@ -3325,22 +3328,29 @@
lg = ac->ac_lg;
if (lg == NULL)
return 0;
+ order = fls(ac->ac_o_ex.fe_len) - 1;
+ if (order > PREALLOC_TB_SIZE - 1)
+ /* The max size of hash table is PREALLOC_TB_SIZE */
+ order = PREALLOC_TB_SIZE - 1;
- rcu_read_lock();
- list_for_each_entry_rcu(pa, &lg->lg_prealloc_list, pa_inode_list) {
- 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);
+ for (i = order; i < PREALLOC_TB_SIZE; i++) {
+ rcu_read_lock();
+ list_for_each_entry_rcu(pa, &lg->lg_prealloc_list[i],
+ pa_inode_list) {
+ 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;
+ }
spin_unlock(&pa->pa_lock);
- ac->ac_criteria = 20;
- rcu_read_unlock();
- return 1;
}
- spin_unlock(&pa->pa_lock);
+ rcu_read_unlock();
}
- rcu_read_unlock();
-
return 0;
}
@@ -3563,6 +3573,7 @@
pa->pa_free = pa->pa_len;
atomic_set(&pa->pa_count, 1);
spin_lock_init(&pa->pa_lock);
+ INIT_LIST_HEAD(&pa->pa_inode_list);
pa->pa_deleted = 0;
pa->pa_linear = 1;
@@ -3583,10 +3594,10 @@
list_add(&pa->pa_group_list, &grp->bb_prealloc_list);
ext4_unlock_group(sb, ac->ac_b_ex.fe_group);
- spin_lock(pa->pa_obj_lock);
- list_add_tail_rcu(&pa->pa_inode_list, &lg->lg_prealloc_list);
- spin_unlock(pa->pa_obj_lock);
-
+ /*
+ * We will later add the new pa to the right bucket
+ * after updating the pa_free in ext4_mb_release_context
+ */
return 0;
}
@@ -4123,22 +4134,168 @@
}
+static noinline_for_stack void
+ext4_mb_discard_lg_preallocations(struct super_block *sb,
+ struct ext4_locality_group *lg,
+ int order, int total_entries)
+{
+ ext4_group_t group = 0;
+ struct ext4_buddy e4b;
+ struct list_head discard_list;
+ struct ext4_prealloc_space *pa, *tmp;
+ struct ext4_allocation_context *ac;
+
+ mb_debug("discard locality group preallocation\n");
+
+ INIT_LIST_HEAD(&discard_list);
+ ac = kmem_cache_alloc(ext4_ac_cachep, GFP_NOFS);
+
+ spin_lock(&lg->lg_prealloc_lock);
+ list_for_each_entry_rcu(pa, &lg->lg_prealloc_list[order],
+ pa_inode_list) {
+ spin_lock(&pa->pa_lock);
+ if (atomic_read(&pa->pa_count)) {
+ /*
+ * This is the pa that we just used
+ * for block allocation. So don't
+ * free that
+ */
+ spin_unlock(&pa->pa_lock);
+ continue;
+ }
+ if (pa->pa_deleted) {
+ spin_unlock(&pa->pa_lock);
+ continue;
+ }
+ /* only lg prealloc space */
+ BUG_ON(!pa->pa_linear);
+
+ /* seems this one can be freed ... */
+ pa->pa_deleted = 1;
+ spin_unlock(&pa->pa_lock);
+
+ list_del_rcu(&pa->pa_inode_list);
+ list_add(&pa->u.pa_tmp_list, &discard_list);
+
+ total_entries--;
+ if (total_entries <= 5) {
+ /*
+ * we want to keep only 5 entries
+ * allowing it to grow to 8. This
+ * mak sure we don't call discard
+ * soon for this list.
+ */
+ break;
+ }
+ }
+ spin_unlock(&lg->lg_prealloc_lock);
+
+ list_for_each_entry_safe(pa, tmp, &discard_list, u.pa_tmp_list) {
+
+ ext4_get_group_no_and_offset(sb, pa->pa_pstart, &group, NULL);
+ if (ext4_mb_load_buddy(sb, group, &e4b)) {
+ ext4_error(sb, __func__, "Error in loading buddy "
+ "information for %lu\n", group);
+ continue;
+ }
+ ext4_lock_group(sb, group);
+ list_del(&pa->pa_group_list);
+ ext4_mb_release_group_pa(&e4b, pa, ac);
+ ext4_unlock_group(sb, group);
+
+ ext4_mb_release_desc(&e4b);
+ list_del(&pa->u.pa_tmp_list);
+ call_rcu(&(pa)->u.pa_rcu, ext4_mb_pa_callback);
+ }
+ if (ac)
+ kmem_cache_free(ext4_ac_cachep, ac);
+}
+
+/*
+ * We have incremented pa_count. So it cannot be freed at this
+ * point. Also we hold lg_mutex. So no parallel allocation is
+ * possible from this lg. That means pa_free cannot be updated.
+ *
+ * A parallel ext4_mb_discard_group_preallocations is possible.
+ * which can cause the lg_prealloc_list to be updated.
+ */
+
+static void ext4_mb_add_n_trim(struct ext4_allocation_context *ac)
+{
+ int order, added = 0, lg_prealloc_count = 1;
+ struct super_block *sb = ac->ac_sb;
+ struct ext4_locality_group *lg = ac->ac_lg;
+ struct ext4_prealloc_space *tmp_pa, *pa = ac->ac_pa;
+
+ order = fls(pa->pa_free) - 1;
+ if (order > PREALLOC_TB_SIZE - 1)
+ /* The max size of hash table is PREALLOC_TB_SIZE */
+ order = PREALLOC_TB_SIZE - 1;
+ /* Add the prealloc space to lg */
+ rcu_read_lock();
+ list_for_each_entry_rcu(tmp_pa, &lg->lg_prealloc_list[order],
+ pa_inode_list) {
+ spin_lock(&tmp_pa->pa_lock);
+ if (tmp_pa->pa_deleted) {
+ spin_unlock(&pa->pa_lock);
+ continue;
+ }
+ if (!added && pa->pa_free < tmp_pa->pa_free) {
+ /* Add to the tail of the previous entry */
+ list_add_tail_rcu(&pa->pa_inode_list,
+ &tmp_pa->pa_inode_list);
+ added = 1;
+ /*
+ * we want to count the total
+ * number of entries in the list
+ */
+ }
+ spin_unlock(&tmp_pa->pa_lock);
+ lg_prealloc_count++;
+ }
+ if (!added)
+ list_add_tail_rcu(&pa->pa_inode_list,
+ &lg->lg_prealloc_list[order]);
+ rcu_read_unlock();
+
+ /* Now trim the list to be not more than 8 elements */
+ if (lg_prealloc_count > 8) {
+ ext4_mb_discard_lg_preallocations(sb, lg,
+ order, lg_prealloc_count);
+ return;
+ }
+ return ;
+}
+
/*
* release all resource we used in allocation
*/
static int ext4_mb_release_context(struct ext4_allocation_context *ac)
{
- if (ac->ac_pa) {
- if (ac->ac_pa->pa_linear) {
+ struct ext4_prealloc_space *pa = ac->ac_pa;
+ if (pa) {
+ if (pa->pa_linear) {
/* see comment in ext4_mb_use_group_pa() */
- spin_lock(&ac->ac_pa->pa_lock);
- ac->ac_pa->pa_pstart += ac->ac_b_ex.fe_len;
- ac->ac_pa->pa_lstart += ac->ac_b_ex.fe_len;
- ac->ac_pa->pa_free -= ac->ac_b_ex.fe_len;
- ac->ac_pa->pa_len -= ac->ac_b_ex.fe_len;
- spin_unlock(&ac->ac_pa->pa_lock);
+ spin_lock(&pa->pa_lock);
+ pa->pa_pstart += ac->ac_b_ex.fe_len;
+ pa->pa_lstart += ac->ac_b_ex.fe_len;
+ pa->pa_free -= ac->ac_b_ex.fe_len;
+ pa->pa_len -= ac->ac_b_ex.fe_len;
+ spin_unlock(&pa->pa_lock);
+ /*
+ * We want to add the pa to the right bucket.
+ * Remove it from the list and while adding
+ * make sure the list to which we are adding
+ * doesn't grow big.
+ */
+ if (likely(pa->pa_free)) {
+ spin_lock(pa->pa_obj_lock);
+ list_del_rcu(&pa->pa_inode_list);
+ spin_unlock(pa->pa_obj_lock);
+ ext4_mb_add_n_trim(ac);
+ }
}
- ext4_mb_put_pa(ac, ac->ac_sb, ac->ac_pa);
+ ext4_mb_put_pa(ac, ac->ac_sb, pa);
}
if (ac->ac_bitmap_page)
page_cache_release(ac->ac_bitmap_page);