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");
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