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Message-Id: <6c7d1e3005dbec5483bdb9b7b60071175bf7bf70.1688811201.git.christophe.jaillet@wanadoo.fr>
Date: Sat, 8 Jul 2023 12:13:45 +0200
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Rafael J. Wysocki" <rafael@...nel.org>
Cc: linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
Christophe JAILLET <christophe.jaillet@...adoo.fr>
Subject: [PATCH] kobject: Reorder fields in 'struct kobject'
Group some variables based on their sizes to reduce hole and avoid padding.
On x86_64, this shrinks the size of 'struct kobject' from 256 to 244 bytes.
This structure is often included in some other structures. So these other
structures will also benefit from this 8 bytes saving.
This is especially nice for structure like 'cma_kobject' or 'class_dir'
that are now 256 bytes long. When they are kzalloc()'ed, 256 bytes are
allocated, instead of 512.
Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
---
Try to see how often this is included in another struct. Certainly not
perfect, but gives an idea.
git grep -P \\tstruct\ kobj[^*]*$ | wc -l
163
Using pahole
Before:
======
struct kobject {
const char * name; /* 0 8 */
struct list_head entry; /* 8 16 */
struct kobject * parent; /* 24 8 */
struct kset * kset; /* 32 8 */
const struct kobj_type * ktype; /* 40 8 */
struct kernfs_node * sd; /* 48 8 */
struct kref kref; /* 56 4 */
/* XXX 4 bytes hole, try to pack */
/* --- cacheline 1 boundary (64 bytes) --- */
struct delayed_work release; /* 64 184 */
/* XXX last struct has 4 bytes of padding */
/* --- cacheline 3 boundary (192 bytes) was 56 bytes ago --- */
unsigned int state_initialized:1; /* 248: 0 4 */
unsigned int state_in_sysfs:1; /* 248: 1 4 */
unsigned int state_add_uevent_sent:1; /* 248: 2 4 */
unsigned int state_remove_uevent_sent:1; /* 248: 3 4 */
unsigned int uevent_suppress:1; /* 248: 4 4 */
/* size: 256, cachelines: 4, members: 13 */
/* sum members: 244, holes: 1, sum holes: 4 */
/* sum bitfield members: 5 bits (0 bytes) */
/* padding: 4 */
/* paddings: 1, sum paddings: 4 */
/* bit_padding: 27 bits */
};
After:
=====
struct kobject {
const char * name; /* 0 8 */
struct list_head entry; /* 8 16 */
struct kobject * parent; /* 24 8 */
struct kset * kset; /* 32 8 */
const struct kobj_type * ktype; /* 40 8 */
struct kernfs_node * sd; /* 48 8 */
struct kref kref; /* 56 4 */
unsigned int state_initialized:1; /* 60: 0 4 */
unsigned int state_in_sysfs:1; /* 60: 1 4 */
unsigned int state_add_uevent_sent:1; /* 60: 2 4 */
unsigned int state_remove_uevent_sent:1; /* 60: 3 4 */
unsigned int uevent_suppress:1; /* 60: 4 4 */
/* XXX 27 bits hole, try to pack */
/* --- cacheline 1 boundary (64 bytes) --- */
struct delayed_work release; /* 64 184 */
/* XXX last struct has 4 bytes of padding */
/* size: 248, cachelines: 4, members: 13 */
/* sum members: 244 */
/* sum bitfield members: 5 bits, bit holes: 1, sum bit holes: 27 bits */
/* paddings: 1, sum paddings: 4 */
/* last cacheline: 56 bytes */
};
---
include/linux/kobject.h | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/include/linux/kobject.h b/include/linux/kobject.h
index c392c811d9ad..c30affcc43b4 100644
--- a/include/linux/kobject.h
+++ b/include/linux/kobject.h
@@ -69,14 +69,16 @@ struct kobject {
const struct kobj_type *ktype;
struct kernfs_node *sd; /* sysfs directory entry */
struct kref kref;
-#ifdef CONFIG_DEBUG_KOBJECT_RELEASE
- struct delayed_work release;
-#endif
+
unsigned int state_initialized:1;
unsigned int state_in_sysfs:1;
unsigned int state_add_uevent_sent:1;
unsigned int state_remove_uevent_sent:1;
unsigned int uevent_suppress:1;
+
+#ifdef CONFIG_DEBUG_KOBJECT_RELEASE
+ struct delayed_work release;
+#endif
};
__printf(2, 3) int kobject_set_name(struct kobject *kobj, const char *name, ...);
--
2.34.1
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