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cache: reduce memory waste in struct namecache

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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.
This commit is contained in:
Mateusz Guzik 2020-10-23 15:56:22 +00:00
parent 25fb30bd9a
commit 3862838921
1 changed files with 13 additions and 5 deletions
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18
sys/kern/vfs_cache.c
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@ -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");