[34-longterm 018/260] ext4: check for a good block group before loading buddy pages

Paul Gortmaker
2011-01-02T08:12:53Z

From: Curt Wohlgemuth <curtw@google.com>

commit 8a57d9d61a6e361c7bb159dda797672c1df1a691 upstream.

This adds a new field in ext4_group_info to cache the largest available
block range in a block group; and don't load the buddy pages until *after*
we've done a sanity check on the block group.

With large allocation requests (e.g., fallocate(), 8MiB) and relatively full
partitions, it's easy to have no block groups with a block extent large
enough to satisfy the input request length. This currently causes the loop
during cr == 0 in ext4_mb_regular_allocator() to load the buddy bitmap pages
for EVERY block group. That can be a lot of pages. The patch below allows
us to call ext4_mb_good_group() BEFORE we load the buddy pages (although we
have check again after we lock the block group).

Addresses-Google-Bug: #2578108
Addresses-Google-Bug: #2704453

Signed-off-by: Curt Wohlgemuth <curtw@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
fs/ext4/ext4.h | 1 +
fs/ext4/mballoc.c | 70 +++++++++++++++++++++++++++++++++++++++++++----------
2 files changed, 58 insertions(+), 13 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index bf938cf..d266003 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1678,6 +1678,7 @@ struct ext4_group_info {
ext4_grpblk_t bb_first_free; /* first free block */
ext4_grpblk_t bb_free; /* total free blocks */
ext4_grpblk_t bb_fragments; /* nr of freespace fragments */
+ ext4_grpblk_t bb_largest_free_order;/* order of largest frag in BG */
struct list_head bb_prealloc_list;
#ifdef DOUBLE_CHECK
void *bb_bitmap;
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 4f2d3a9..aa499fe 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -658,6 +658,27 @@ static void ext4_mb_mark_free_simple(struct super_block *sb,
}
}

+/*
+ * Cache the order of the largest free extent we have available in this block
+ * group.
+ */
+static void
+mb_set_largest_free_order(struct super_block *sb, struct ext4_group_info *grp)
+{
+ int i;
+ int bits;
+
+ grp->bb_largest_free_order = -1; /* uninit */
+
+ bits = sb->s_blocksize_bits + 1;
+ for (i = bits; i >= 0; i--) {
+ if (grp->bb_counters[i] > 0) {
+ grp->bb_largest_free_order = i;
+ break;
+ }
+ }
+}
+
static noinline_for_stack
void ext4_mb_generate_buddy(struct super_block *sb,
void *buddy, void *bitmap, ext4_group_t group)
@@ -700,6 +721,7 @@ void ext4_mb_generate_buddy(struct super_block *sb,
*/
grp->bb_free = free;
}
+ mb_set_largest_free_order(sb, grp);

clear_bit(EXT4_GROUP_INFO_NEED_INIT_BIT, &(grp->bb_state));

@@ -725,6 +747,9 @@ void ext4_mb_generate_buddy(struct super_block *sb,
* contain blocks_per_page (PAGE_CACHE_SIZE / blocksize) blocks.
* So it can have information regarding groups_per_page which
* is blocks_per_page/2
+ *
+ * Locking note: This routine takes the block group lock of all groups
+ * for this page; do not hold this lock when calling this routine!
*/

static int ext4_mb_init_cache(struct page *page, char *incore)
@@ -910,6 +935,11 @@ out:
return err;
}

+/*
+ * Locking note: This routine calls ext4_mb_init_cache(), which takes the
+ * block group lock of all groups for this page; do not hold the BG lock when
+ * calling this routine!
+ */
static noinline_for_stack
int ext4_mb_init_group(struct super_block *sb, ext4_group_t group)
{
@@ -1004,6 +1034,11 @@ err:
return ret;
}

+/*
+ * Locking note: This routine calls ext4_mb_init_cache(), which takes the
+ * block group lock of all groups for this page; do not hold the BG lock when
+ * calling this routine!
+ */
static noinline_for_stack int
ext4_mb_load_buddy(struct super_block *sb, ext4_group_t group,
struct ext4_buddy *e4b)
@@ -1299,6 +1334,7 @@ static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,
buddy = buddy2;
} while (1);
}
+ mb_set_largest_free_order(sb, e4b->bd_info);
mb_check_buddy(e4b);
}

@@ -1427,6 +1463,7 @@ static int mb_mark_used(struct ext4_buddy *e4b, struct ext4_free_extent *ex)
e4b->bd_info->bb_counters[ord]++;
e4b->bd_info->bb_counters[ord]++;
}
+ mb_set_largest_free_order(e4b->bd_sb, e4b->bd_info);

mb_set_bits(EXT4_MB_BITMAP(e4b), ex->fe_start, len0);
mb_check_buddy(e4b);
@@ -1821,16 +1858,22 @@ void ext4_mb_scan_aligned(struct ext4_allocation_context *ac,
}
}

+/* This is now called BEFORE we load the buddy bitmap. */
static int ext4_mb_good_group(struct ext4_allocation_context *ac,
ext4_group_t group, int cr)
{
unsigned free, fragments;
- unsigned i, bits;
int flex_size = ext4_flex_bg_size(EXT4_SB(ac->ac_sb));
struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group);

BUG_ON(cr < 0 || cr >= 4);
- BUG_ON(EXT4_MB_GRP_NEED_INIT(grp));
+
+ /* We only do this if the grp has never been initialized */
+ if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
+ int ret = ext4_mb_init_group(ac->ac_sb, group);
+ if (ret)
+ return 0;
+ }

free = grp->bb_free;
fragments = grp->bb_fragments;
@@ -1843,17 +1886,16 @@ static int ext4_mb_good_group(struct ext4_allocation_context *ac,
case 0:
BUG_ON(ac->ac_2order == 0);

+ if (grp->bb_largest_free_order < ac->ac_2order)
+ return 0;
+
/* Avoid using the first bg of a flexgroup for data files */
if ((ac->ac_flags & EXT4_MB_HINT_DATA) &&
(flex_size >= EXT4_FLEX_SIZE_DIR_ALLOC_SCHEME) &&
((group % flex_size) == 0))
return 0;

- bits = ac->ac_sb->s_blocksize_bits + 1;
- for (i = ac->ac_2order; i <= bits; i++)
- if (grp->bb_counters[i] > 0)
- return 1;
- break;
+ return 1;
case 1:
if ((free / fragments) >= ac->ac_g_ex.fe_len)
return 1;
@@ -2024,14 +2066,11 @@ repeat:
group = ac->ac_g_ex.fe_group;

for (i = 0; i < ngroups; group++, i++) {
- struct ext4_group_info *grp;
-
if (group == ngroups)
group = 0;

- /* quick check to skip empty groups */
- grp = ext4_get_group_info(sb, group);
- if (grp->bb_free == 0)
+ /* This now checks without needing the buddy page */
+ if (!ext4_mb_good_group(ac, group, cr))
continue;

err = ext4_mb_load_buddy(sb, group, &e4b);
@@ -2039,8 +2078,12 @@ repeat:
goto out;

ext4_lock_group(sb, group);
+
+ /*
+ * We need to check again after locking the
+ * block group
+ */
if (!ext4_mb_good_group(ac, group, cr)) {
- /* someone did allocation from this group */
ext4_unlock_group(sb, group);
ext4_mb_unload_buddy(&e4b);
continue;
@@ -2253,6 +2296,7 @@ int ext4_mb_add_groupinfo(struct super_block *sb, ext4_group_t group,
INIT_LIST_HEAD(&meta_group_info[i]->bb_prealloc_list);
init_rwsem(&meta_group_info[i]->alloc_sem);
meta_group_info[i]->bb_free_root = RB_ROOT;
+ meta_group_info[i]->bb_largest_free_order = -1; /* uninit */

#ifdef DOUBLE_CHECK
{
--
1.7.3.3