ext4: mitigatin cacheline false sharing in struct ext4_inode_info

hulk inclusion
category: performance
bugzilla: https://gitee.com/openeuler/kernel/issues/I7ADMY

--------------------------------

In the test of execl, shell1 and shell8 of UnixBench, L3 false sharing
occurs between rwsem_try_write_lock_unqueued() and filemap_map_pages().

The offset between address_space.host and address_space.i_mmap_rwsem
is 48. It may occur L3 false sharing. Their offsets in struct ext4_inode_info
is 696 and 744, so when the address of ext4_inode_info after L3 aligned,
it may occur L3 false sharing in the following condition:

[0x00 ~ 0x10] false sharing
[0x18 ~ 0x40] no false sharing
[0x48 ~ 0x80] false sharing

Change the offset of 'vfs_inode' from 320 to 360 in ext4_inode_info and
make the address of ext4_inode_info L3 aligned, so the offset of host
and i_mmap_rwsem in ext4_inode_info is changed to 736 and 784, it can
make them in different L3 to avoid false sharing.

./Run -c 96 -i 3 execl

Before this patch:
System Benchmarks Partial Index              BASELINE       RESULT    INDEX
Execl Throughput                                 43.0      24238.0   5636.8
                                                                   ========
System Benchmarks Index Score (Partial Only)                         5636.8

After this patch:
System Benchmarks Partial Index              BASELINE       RESULT    INDEX
Execl Throughput                                 43.0      29363.7   6828.8
                                                                   ========
System Benchmarks Index Score (Partial Only)                         6828.8
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

fs/ext4/Kconfig

@@ -117,3 +117,12 @@ config EXT4_KUNIT_TESTS
 	  to the KUnit documentation in Documentation/dev-tools/kunit/.
 
 	  If unsure, say N.
+
+config EXT4_MITIGATION_FALSE_SHARING
+	bool "mitigation false sharing in ext4 inode"
+	depends on EXT4_FS
+	default n
+	help
+	  Enable this to mitigation cacheline false sharing in ext4 inode info.
+
+	  If unsure, say N.

fs/ext4/ext4.h

@@ -1090,7 +1090,9 @@ struct ext4_inode_info {
 	 * to occasionally drop it.
 	 */
 	struct rw_semaphore i_mmap_sem;
+#ifndef CONFIG_EXT4_MITIGATION_FALSE_SHARING
 	struct inode vfs_inode;
+#endif
 	struct jbd2_inode *jinode;
 
 	spinlock_t i_raw_lock;	/* protects updates to the raw inode */
@@ -1103,6 +1105,9 @@ struct ext4_inode_info {
 
 	/* mballoc */
 	atomic_t i_prealloc_active;
+#ifdef CONFIG_EXT4_MITIGATION_FALSE_SHARING
+	struct inode vfs_inode;
+#endif
 	struct list_head i_prealloc_list;
 	spinlock_t i_prealloc_lock;
 

fs/ext4/super.c

@@ -1420,7 +1420,11 @@ static void init_once(void *foo)
 static int __init init_inodecache(void)
 {
 	ext4_inode_cachep = kmem_cache_create_usercopy("ext4_inode_cache",
+#ifdef CONFIG_EXT4_MITIGATION_FALSE_SHARING
+				sizeof(struct ext4_inode_info), 128,
+#else
 				sizeof(struct ext4_inode_info), 0,
+#endif
 				(SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD|
 					SLAB_ACCOUNT),
 				offsetof(struct ext4_inode_info, i_data),