linux-ext4 - [PATCH] ext4: Adjust the layout of the ext4_inode

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Message-Id: <20240603131524.324224-1-sunjunchao2870@gmail.com>
Date: Mon,  3 Jun 2024 21:15:24 +0800
From: Junchao Sun <sunjunchao2870@...il.com>
To: linux-ext4@...r.kernel.org
Cc: tytso@....edu,
	adilger.kernel@...ger.ca,
	jack@...e.cz,
	Junchao Sun <sunjunchao2870@...il.com>
Subject: [PATCH] ext4: Adjust the layout of the ext4_inode_info structure to save memory.

Using pahole, we can see that there are some padding holes
in the current ext4_inode_info structure. Adjusting the
layout of ext4_inode_info can reduce these holes,
resulting in the size of the structure decreasing
from 2424 bytes to 2408 bytes.

Signed-off-by: Junchao Sun <sunjunchao2870@...il.com>
---
 fs/ext4/ext4.h | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 023571f8dd1b..42bcd4f749a8 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1055,6 +1055,7 @@ struct ext4_inode_info {
 
 	/* Number of ongoing updates on this inode */
 	atomic_t  i_fc_updates;
+	atomic_t i_unwritten; /* Nr. of inflight conversions pending */
 
 	/* Fast commit wait queue for this inode */
 	wait_queue_head_t i_fc_wait;
@@ -1103,6 +1104,10 @@ struct ext4_inode_info {
 
 	/* mballoc */
 	atomic_t i_prealloc_active;
+
+	/* allocation reservation info for delalloc */
+	/* In case of bigalloc, this refer to clusters rather than blocks */
+	unsigned int i_reserved_data_blocks;
 	struct rb_root i_prealloc_node;
 	rwlock_t i_prealloc_lock;
 
@@ -1119,10 +1124,6 @@ struct ext4_inode_info {
 	/* ialloc */
 	ext4_group_t	i_last_alloc_group;
 
-	/* allocation reservation info for delalloc */
-	/* In case of bigalloc, this refer to clusters rather than blocks */
-	unsigned int i_reserved_data_blocks;
-
 	/* pending cluster reservations for bigalloc file systems */
 	struct ext4_pending_tree i_pending_tree;
 
@@ -1146,7 +1147,6 @@ struct ext4_inode_info {
 	 */
 	struct list_head i_rsv_conversion_list;
 	struct work_struct i_rsv_conversion_work;
-	atomic_t i_unwritten; /* Nr. of inflight conversions pending */
 
 	spinlock_t i_block_reservation_lock;
 
-- 
2.39.2