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cache: avoid hardcoded zone alignment

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Previously, this was underaligned on CHERI system where pointers are
larger than time_t.

Use the alignment of struct namecache_ts which picks up time_t via strut
timespec and pointers via struct namecache.  This arguably overaligns
cache_zone_small and cache_zone_large on i386 kernels, but I suspect the
actual microarchitectures most i386 binaries are run on do better with
64-bit alignment.

Reviewed by:	olce, markj
Effort:		CHERI upstreaming
Sponsored by:	Innovate UK
Fixes:		cf8ac0de81 ("cache: reduce zone alignment to 8 bytes")
Differential Revision:	https://reviews.freebsd.org/D54376
This commit is contained in:
Brooks Davis
2026-01-09 14:15:22 +00:00
parent 821c6c43a3
commit fb0bdbea2e
1 changed files with 23 additions and 21 deletions
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sys/kern/vfs_cache.c
+23 -21
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@@ -384,14 +384,10 @@ struct namecache {
};
/*
* struct namecache_ts repeats struct namecache layout up to the
* nc_nlen member.
* struct namecache_ts is used in place of struct namecache when time(s) need
* to be stored. The nc_dotdottime field is used when a cache entry is mapping
* both a non-dotdot directory name plus dotdot for the directory's
* parent.
*
* See below for alignment requirement.
*/
struct namecache_ts {
struct timespec nc_time; /* timespec provided by fs */
@@ -404,12 +400,10 @@ struct namecache_ts {
TAILQ_HEAD(cache_freebatch, namecache);
/*
* At least mips n32 performs 64-bit accesses to timespec as found
* in namecache_ts and requires them to be aligned. Since others
* may be in the same spot suffer a little bit and enforce the
* alignment for everyone. Note this is a nop for 64-bit platforms.
* Ensure all zones are sufficently aligned to hold both
* struct namecache and struct namecache_ts.
*/
#define CACHE_ZONE_ALIGNMENT UMA_ALIGNOF(time_t)
#define CACHE_ZONE_ALIGN_MASK UMA_ALIGNOF(struct namecache_ts)
/*
* TODO: the initial value of CACHE_PATH_CUTOFF was inherited from the
@@ -432,15 +426,23 @@ TAILQ_HEAD(cache_freebatch, namecache);
#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)
#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");
_Static_assert((CACHE_ZONE_LARGE_SIZE % (CACHE_ZONE_ALIGNMENT + 1)) == 0, "bad zone size");
_Static_assert((CACHE_ZONE_LARGE_TS_SIZE % (CACHE_ZONE_ALIGNMENT + 1)) == 0, "bad zone size");
_Static_assert((CACHE_ZONE_SMALL_SIZE % (CACHE_ZONE_ALIGN_MASK + 1)) == 0,
"bad zone size");
_Static_assert((CACHE_ZONE_SMALL_TS_SIZE % (CACHE_ZONE_ALIGN_MASK + 1)) == 0,
"bad zone size");
_Static_assert((CACHE_ZONE_LARGE_SIZE % (CACHE_ZONE_ALIGN_MASK + 1)) == 0,
"bad zone size");
_Static_assert((CACHE_ZONE_LARGE_TS_SIZE % (CACHE_ZONE_ALIGN_MASK + 1)) == 0,
"bad zone size");
#define nc_vp n_un.nu_vp
#define nc_neg n_un.nu_neg
@@ -2785,13 +2787,13 @@ nchinit(void *dummy __unused)
u_int i;
cache_zone_small = uma_zcreate("S VFS Cache", CACHE_ZONE_SMALL_SIZE,
NULL, NULL, NULL, NULL, CACHE_ZONE_ALIGNMENT, UMA_ZONE_ZINIT);
NULL, NULL, NULL, NULL, CACHE_ZONE_ALIGN_MASK, UMA_ZONE_ZINIT);
cache_zone_small_ts = uma_zcreate("STS VFS Cache", CACHE_ZONE_SMALL_TS_SIZE,
NULL, NULL, NULL, NULL, CACHE_ZONE_ALIGNMENT, UMA_ZONE_ZINIT);
NULL, NULL, NULL, NULL, CACHE_ZONE_ALIGN_MASK, UMA_ZONE_ZINIT);
cache_zone_large = uma_zcreate("L VFS Cache", CACHE_ZONE_LARGE_SIZE,
NULL, NULL, NULL, NULL, CACHE_ZONE_ALIGNMENT, UMA_ZONE_ZINIT);
NULL, NULL, NULL, NULL, CACHE_ZONE_ALIGN_MASK, UMA_ZONE_ZINIT);
cache_zone_large_ts = uma_zcreate("LTS VFS Cache", CACHE_ZONE_LARGE_TS_SIZE,
NULL, NULL, NULL, NULL, CACHE_ZONE_ALIGNMENT, UMA_ZONE_ZINIT);
NULL, NULL, NULL, NULL, CACHE_ZONE_ALIGN_MASK, UMA_ZONE_ZINIT);
VFS_SMR_ZONE_SET(cache_zone_small);
VFS_SMR_ZONE_SET(cache_zone_small_ts);