[PATCH] 9p: optimize p9_fcall struct

[PATCH] 9p: optimize p9_fcall struct

[Dominique Martinet]

p9_fcall has a 1 byte hole followed by more data and then a single byte
element:

struct p9_fcall {
	u32                        size;                 /*     0     4 */
	u8                         id;                   /*     4     1 */

	/* XXX 1 byte hole, try to pack */

	u16                        tag;                  /*     6     2 */
	size_t                     offset;               /*     8     8 */
	size_t                     capacity;             /*    16     8 */
	struct kmem_cache *        cache;                /*    24     8 */
	u8 *                       sdata;                /*    32     8 */
	bool                       zc;                   /*    40     1 */

	/* size: 48, cachelines: 1, members: 8 */
	/* sum members: 40, holes: 1, sum holes: 1 */
	/* padding: 7 */
	/* last cacheline: 48 bytes */
};

move `zc` up to optimize it:

struct p9_fcall {
	u32                        size;                 /*     0     4 */
	u8                         id;                   /*     4     1 */
	bool                       zc;                   /*     5     1 */
	u16                        tag;                  /*     6     2 */
	size_t                     offset;               /*     8     8 */
	size_t                     capacity;             /*    16     8 */
	struct kmem_cache *        cache;                /*    24     8 */
	u8 *                       sdata;                /*    32     8 */

	/* size: 40, cachelines: 1, members: 8 */
	/* last cacheline: 40 bytes */
};

This in turn also makes p9_req_t 16 bytes smaller (152 -> 136) as it
contains two of these.

Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
---
 include/net/9p/9p.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/net/9p/9p.h b/include/net/9p/9p.h
index 22ab7486795d..067e8a3b38d0 100644
--- a/include/net/9p/9p.h
+++ b/include/net/9p/9p.h
@@ -581,6 +581,7 @@ struct p9_rstatfs {
 struct p9_fcall {
 	u32 size;
 	u8 id;
+	bool zc;
 	u16 tag;
 
 	size_t offset;
@@ -588,7 +589,6 @@ struct p9_fcall {
 
 	struct kmem_cache *cache;
 	u8 *sdata;
-	bool zc;
 };
 
 int p9_errstr2errno(char *errstr, int len);
-- 
2.56.0

Re: [PATCH] 9p: optimize p9_fcall struct

[sashiko-bot]

> p9_fcall has a 1 byte hole followed by more data and then a single byte
> element:
> 
> struct p9_fcall {
> 	u32                        size;                 /*     0     4 */
> 	u8                         id;                   /*     4     1 */
> 
> 	/* XXX 1 byte hole, try to pack */
> 
> 	u16                        tag;                  /*     6     2 */
> 	size_t                     offset;               /*     8     8 */
> 	size_t                     capacity;             /*    16     8 */
> 	struct kmem_cache *        cache;                /*    24     8 */
> 	u8 *                       sdata;                /*    32     8 */
> 	bool                       zc;                   /*    40     1 */
> [ ... ]
> 
> This in turn also makes p9_req_t 16 bytes smaller (152 -> 136) as it
> contains two of these.
> 
> Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>

Sashiko has reviewed this patch and found no issues.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261029060014.3-1-asmadeus@codewreck.org?part=1