svn commit: r366976 - head/sys/kern

[Mateusz Guzik]

Author: mjg
Date: Fri Oct 23 15:56:22 2020
New Revision: 366976
URL: https://svnweb.freebsd.org/changeset/base/366976

Log:
  cache: reduce memory waste in struct namecache
  
  The previous scheme for calculating the total size was doing sizeof
  on the struct and then adding the wanted space for the buffer.
  
  nc_name is at offset 58 while sizeof(struct namecache) is 64.
  With CACHE_PATH_CUTOFF of 39 bytes and 1 byte of padding we were
  allocating 104 bytes for the entry and never accounting for the 6
  byte padding, wasting that space.

Modified:
  head/sys/kern/vfs_cache.c

Modified: head/sys/kern/vfs_cache.c
==============================================================================
--- head/sys/kern/vfs_cache.c	Fri Oct 23 15:50:49 2020	(r366975)
+++ head/sys/kern/vfs_cache.c	Fri Oct 23 15:56:22 2020	(r366976)
@@ -162,6 +162,7 @@ struct	namecache_ts {
 	struct	timespec nc_time;	/* timespec provided by fs */
 	struct	timespec nc_dotdottime;	/* dotdot timespec provided by fs */
 	int	nc_ticks;		/* ticks value when entry was added */
+	int	nc_pad;
 	struct namecache nc_nc;
 };
 
@@ -172,12 +173,19 @@ struct	namecache_ts {
  * alignment for everyone. Note this is a nop for 64-bit platforms.
  */
 #define CACHE_ZONE_ALIGNMENT	UMA_ALIGNOF(time_t)
-#define	CACHE_PATH_CUTOFF	39
 
-#define CACHE_ZONE_SMALL_SIZE		(sizeof(struct namecache) + CACHE_PATH_CUTOFF + 1)
-#define CACHE_ZONE_SMALL_TS_SIZE	(sizeof(struct namecache_ts) + CACHE_PATH_CUTOFF + 1)
-#define CACHE_ZONE_LARGE_SIZE		(sizeof(struct namecache) + NAME_MAX + 1)
-#define CACHE_ZONE_LARGE_TS_SIZE	(sizeof(struct namecache_ts) + NAME_MAX + 1)
+#ifdef __LP64__
+#define	CACHE_PATH_CUTOFF	45
+#define	CACHE_LARGE_PAD		6
+#else
+#define	CACHE_PATH_CUTOFF	41
+#define	CACHE_LARGE_PAD		2
+#endif
+
+#define CACHE_ZONE_SMALL_SIZE		(offsetof(struct namecache, nc_name) + CACHE_PATH_CUTOFF + 1)
+#define CACHE_ZONE_SMALL_TS_SIZE	(offsetof(struct namecache_ts, nc_nc) + CACHE_ZONE_SMALL_SIZE)
+#define CACHE_ZONE_LARGE_SIZE		(offsetof(struct namecache, nc_name) + NAME_MAX + 1 + CACHE_LARGE_PAD)
+#define CACHE_ZONE_LARGE_TS_SIZE	(offsetof(struct namecache_ts, nc_nc) + CACHE_ZONE_LARGE_SIZE)
 
 _Static_assert((CACHE_ZONE_SMALL_SIZE % (CACHE_ZONE_ALIGNMENT + 1)) == 0, "bad zone size");
 _Static_assert((CACHE_ZONE_SMALL_TS_SIZE % (CACHE_ZONE_ALIGNMENT + 1)) == 0, "bad zone size");