git: 1b425afa8d5f - main - cache: avoid hardcoded CACHE_PATH_CUTOFF

The branch main has been updated by brooks:

URL: https://cgit.FreeBSD.org/src/commit/?id=1b425afa8d5fb611b17f951e5099c177fd97ffea

commit 1b425afa8d5fb611b17f951e5099c177fd97ffea
Author:     Brooks Davis <brooks@FreeBSD.org>
AuthorDate: 2026-01-09 14:15:43 +0000
Commit:     Brooks Davis <brooks@FreeBSD.org>
CommitDate: 2026-01-09 14:15:43 +0000

    cache: avoid hardcoded CACHE_PATH_CUTOFF
    
    Compute the cutoff at compile time instead which will avoid the need
    for a CHERI case.
    
    Correct the comment about CACHE_PATH_CUTOFF.  It dates to 5.2.0 not 4.4
    BSD.  Historic values are:
    
    32 - introduced (c2935410f6d5f)
    35 - NUL terminated and bumped (5d5c174869104)
    39 - sized to alignment (bb48255cf5eff)
    45 - bumped to improve efficency on 64-bit (3862838921eb8)
    
    No functional change.
    
    Reviewed by:    markj
    Suggested by:   jhb
    Effort:         CHERI upstreaming
    Sponsored by:   DARPA, AFRL
    Differential Revision:  https://reviews.freebsd.org/D54554
---
 sys/kern/vfs_cache.c | 32 ++++++++++++++++++--------------
 1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/sys/kern/vfs_cache.c b/sys/kern/vfs_cache.c
index 404234861710..3f8591bd0ba7 100644
--- a/sys/kern/vfs_cache.c
+++ b/sys/kern/vfs_cache.c
@@ -406,31 +406,35 @@ TAILQ_HEAD(cache_freebatch, namecache);
 #define CACHE_ZONE_ALIGN_MASK	UMA_ALIGNOF(struct namecache_ts)
 
 /*
- * TODO: the initial value of CACHE_PATH_CUTOFF was inherited from the
- * 4.4 BSD codebase. Later on struct namecache was tweaked to become
- * smaller and the value was bumped to retain the total size, but it
- * was never re-evaluated for suitability. A simple test counting
- * lengths during package building shows that the value of 45 covers
- * about 86% of all added entries, reaching 99% at 65.
+ * TODO: CACHE_PATH_CUTOFF was initially introduced with an arbitrary
+ * value of 32 in FreeBSD 5.2.0.  It was bumped to 35 and the path was
+ * NUL terminated with the introduction of DTrace probes.  Later, it was
+ * expanded to match the alignment allowing an increase to 39, but it
+ * was not re-evaluated for suitability.  It was again bumped to 45 on
+ * 64-bit systems and 41 on 32-bit systems (the current values, now
+ * computed at compile time rather than hardcoded).  A simple test
+ * counting lengths during package building in 2020 showed that the
+ * value of 45 covers about 86% of all added entries, reaching 99%
+ * at 65.
  *
  * Regardless of the above, use of dedicated zones instead of malloc may be
  * inducing additional waste. This may be hard to address as said zones are
  * tied to VFS SMR. Even if retaining them, the current split should be
  * re-evaluated.
  */
-#ifdef __LP64__
-#define	CACHE_PATH_CUTOFF	45
-#else
-#define	CACHE_PATH_CUTOFF	41
-#endif
+#define CACHE_PATH_CUTOFF_MIN    40
+#define CACHE_STRUCT_LEN(pathlen)	\
+    (offsetof(struct namecache, nc_name) + (pathlen) + 1)
+#define CACHE_PATH_CUTOFF						\
+    (roundup2(CACHE_STRUCT_LEN(CACHE_PATH_CUTOFF_MIN),			\
+    _Alignof(struct namecache_ts)) - CACHE_STRUCT_LEN(0))
 
 #define CACHE_ZONE_SMALL_SIZE						\
-    (offsetof(struct namecache, nc_name) + CACHE_PATH_CUTOFF + 1)
+    CACHE_STRUCT_LEN(CACHE_PATH_CUTOFF)
 #define CACHE_ZONE_SMALL_TS_SIZE					\
     (offsetof(struct namecache_ts, nc_nc) + CACHE_ZONE_SMALL_SIZE)
 #define CACHE_ZONE_LARGE_SIZE						\
-    roundup2(offsetof(struct namecache, nc_name) + NAME_MAX + 1,	\
-    _Alignof(struct namecache_ts))
+    roundup2(CACHE_STRUCT_LEN(NAME_MAX), _Alignof(struct namecache_ts))
 #define CACHE_ZONE_LARGE_TS_SIZE					\
     (offsetof(struct namecache_ts, nc_nc) + CACHE_ZONE_LARGE_SIZE)