ext4: Add allocation criteria 1.5 (CR1_5)
CR1_5 aims to optimize allocations which can't be satisfied in CR1. The
fact that we couldn't find a group in CR1 suggests that it would be
difficult to find a continuous extent to compleltely satisfy our
allocations. So before falling to the slower CR2, in CR1.5 we
proactively trim the the preallocations so we can find a group with
(free / fragments) big enough. This speeds up our allocation at the
cost of slightly reduced preallocation.
The patch also adds a new sysfs tunable:
* /sys/fs/ext4/<partition>/mb_cr1_5_max_trim_order
This controls how much CR1.5 can trim a request before falling to CR2.
For example, for a request of order 7 and max trim order 2, CR1.5 can
trim this upto order 5.
Suggested-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Link: https://lore.kernel.org/r/150fdf65c8e4cc4dba71e020ce0859bcf636a5ff.1685449706.git.ojaswin@linux.ibm.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/fs/ext4/mballoc.h b/fs/ext4/mballoc.h
index acfdc204..bddc033 100644
--- a/fs/ext4/mballoc.h
+++ b/fs/ext4/mballoc.h
@@ -86,6 +86,13 @@
#define MB_DEFAULT_LINEAR_SCAN_THRESHOLD 16
/*
+ * The maximum order upto which CR1.5 can trim a particular allocation request.
+ * Example, if we have an order 7 request and max trim order of 3, CR1.5 can
+ * trim this upto order 4.
+ */
+#define MB_DEFAULT_CR1_5_TRIM_ORDER 3
+
+/*
* Number of valid buddy orders
*/
#define MB_NUM_ORDERS(sb) ((sb)->s_blocksize_bits + 2)
@@ -179,6 +186,12 @@ struct ext4_allocation_context {
/* copy of the best found extent taken before preallocation efforts */
struct ext4_free_extent ac_f_ex;
+ /*
+ * goal len can change in CR1.5, so save the original len. This is
+ * used while adjusting the PA window and for accounting.
+ */
+ ext4_grpblk_t ac_orig_goal_len;
+
__u32 ac_groups_considered;
__u32 ac_flags; /* allocation hints */
__u16 ac_groups_scanned;
