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Date:      Wed, 5 Aug 2020 09:24:38 +0000 (UTC)
From:      Mateusz Guzik <mjg@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r363891 - head/sys/kern
Message-ID:  <202008050924.0759Oc3H010909@repo.freebsd.org>
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Author: mjg
Date: Wed Aug  5 09:24:38 2020
New Revision: 363891
URL: https://svnweb.freebsd.org/changeset/base/363891

Log:
  cache: reduce zone alignment to 8 bytes
  
  It used to be sizeof of the given struct to accomodate for 32 bit mips
  doing 64 bit loads, but the same can be achieved with requireing just
  64 bit alignment.
  
  While here reorder struct namecache so that most commonly used fields
  are closer.

Modified:
  head/sys/kern/vfs_cache.c

Modified: head/sys/kern/vfs_cache.c
==============================================================================
--- head/sys/kern/vfs_cache.c	Wed Aug  5 09:24:00 2020	(r363890)
+++ head/sys/kern/vfs_cache.c	Wed Aug  5 09:24:38 2020	(r363891)
@@ -122,9 +122,9 @@ _Static_assert(sizeof(struct negstate) <= sizeof(struc
     "the state must fit in a union with a pointer without growing it");
 
 struct	namecache {
-	CK_LIST_ENTRY(namecache) nc_hash;/* hash chain */
 	LIST_ENTRY(namecache) nc_src;	/* source vnode list */
 	TAILQ_ENTRY(namecache) nc_dst;	/* destination vnode list */
+	CK_LIST_ENTRY(namecache) nc_hash;/* hash chain */
 	struct	vnode *nc_dvp;		/* vnode of parent of name */
 	union {
 		struct	vnode *nu_vp;	/* vnode the name refers to */
@@ -142,6 +142,8 @@ struct	namecache {
  * 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 */
@@ -150,6 +152,14 @@ struct	namecache_ts {
 	struct namecache nc_nc;
 };
 
+/*
+ * 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.
+ */
+#define CACHE_ZONE_ALIGNMENT	UMA_ALIGNOF(time_t)
+
 #define	nc_vp		n_un.nu_vp
 #define	nc_neg		n_un.nu_neg
 
@@ -2053,19 +2063,19 @@ nchinit(void *dummy __unused)
 
 	cache_zone_small = uma_zcreate("S VFS Cache",
 	    sizeof(struct namecache) + CACHE_PATH_CUTOFF + 1,
-	    NULL, NULL, NULL, NULL, UMA_ALIGNOF(struct namecache),
+	    NULL, NULL, NULL, NULL, CACHE_ZONE_ALIGNMENT,
 	    UMA_ZONE_ZINIT);
 	cache_zone_small_ts = uma_zcreate("STS VFS Cache",
 	    sizeof(struct namecache_ts) + CACHE_PATH_CUTOFF + 1,
-	    NULL, NULL, NULL, NULL, UMA_ALIGNOF(struct namecache_ts),
+	    NULL, NULL, NULL, NULL, CACHE_ZONE_ALIGNMENT,
 	    UMA_ZONE_ZINIT);
 	cache_zone_large = uma_zcreate("L VFS Cache",
 	    sizeof(struct namecache) + NAME_MAX + 1,
-	    NULL, NULL, NULL, NULL, UMA_ALIGNOF(struct namecache),
+	    NULL, NULL, NULL, NULL, CACHE_ZONE_ALIGNMENT,
 	    UMA_ZONE_ZINIT);
 	cache_zone_large_ts = uma_zcreate("LTS VFS Cache",
 	    sizeof(struct namecache_ts) + NAME_MAX + 1,
-	    NULL, NULL, NULL, NULL, UMA_ALIGNOF(struct namecache_ts),
+	    NULL, NULL, NULL, NULL, CACHE_ZONE_ALIGNMENT,
 	    UMA_ZONE_ZINIT);
 
 	VFS_SMR_ZONE_SET(cache_zone_small);

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