The default group preallocation size had been previously set to 512
blocks/clusters, regardless of the block/cluster size. This is
probably too big for large cluster sizes. So adjust the default so
that it is 2 megabytes or 32 clusters, whichever is larger.
Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
---
fs/ext4/mballoc.c | 18 ++++++++++++++++--
1 files changed, 16 insertions(+), 2 deletions(-)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 48172a1..2d23d0a 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -126,7 +126,8 @@
* list. In case of inode preallocation we follow a list of heuristics
* based on file size. This can be found in ext4_mb_normalize_request. If
* we are doing a group prealloc we try to normalize the request to
- * sbi->s_mb_group_prealloc. Default value of s_mb_group_prealloc is
+ * sbi->s_mb_group_prealloc. The default value of s_mb_group_prealloc is
+ * dependent on the cluster size; for non-bigalloc file systems, it is
* 512 blocks. This can be tuned via
* /sys/fs/ext4/<partition/mb_group_prealloc. The value is represented in
* terms of number of blocks. If we have mounted the file system with -O
@@ -2471,7 +2472,20 @@ int ext4_mb_init(struct super_block *sb, int needs_recovery)
sbi->s_mb_stats = MB_DEFAULT_STATS;
sbi->s_mb_stream_request = MB_DEFAULT_STREAM_THRESHOLD;
sbi->s_mb_order2_reqs = MB_DEFAULT_ORDER2_REQS;
- sbi->s_mb_group_prealloc = MB_DEFAULT_GROUP_PREALLOC;
+ /*
+ * The default group preallocation is 512, which for 4k block
+ * sizes translates to 2 megabytes. However for bigalloc file
+ * systems, this is probably too big (i.e, if the cluster size
+ * is 1 megabyte, then group preallocation size becomes half a
+ * gigabyte!). As a default, we will keep a two megabyte
+ * group pralloc size for cluster sizes up to 64k, and after
+ * that, we will force a minimum group preallocation size of
+ * 32 clusters. This translates to 8 megs when the cluster
+ * size is 256k, and 32 megs when the cluster size is 1 meg,
+ * which seems reasonable as a default.
+ */
+ sbi->s_mb_group_prealloc = max(MB_DEFAULT_GROUP_PREALLOC >>
+ sbi->s_cluster_bits, 32);
sbi->s_locality_groups = alloc_percpu(struct ext4_locality_group);
if (sbi->s_locality_groups == NULL) {
--
1.7.4.1.22.gec8e1.dirty
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