Author: mjg
Date: Sun Sep 4 08:58:35 2016
New Revision: 305379
URL: https://svnweb.freebsd.org/changeset/base/305379
Log:
cache: manage negative entry list with a dedicated lock
Since negative entries are managed with a LRU list, a hit requires a
modificaton.
Currently the code tries to upgrade the global lock if needed and is
forced to retry the lookup if it fails.
Provide a dedicated lock for use when the cache is only shared-locked.
Reviewed by: kib
MFC after: 1 week
Modified:
head/sys/kern/vfs_cache.c
Modified: head/sys/kern/vfs_cache.c
==============================================================================
--- head/sys/kern/vfs_cache.c Sun Sep 4 08:55:15 2016 (r305378)
+++ head/sys/kern/vfs_cache.c Sun Sep 4 08:58:35 2016 (r305379)
@@ -186,6 +186,9 @@ RW_SYSINIT(vfscache, &cache_lock, "Name
#define CACHE_WLOCK() rw_wlock(&cache_lock)
#define CACHE_WUNLOCK() rw_wunlock(&cache_lock)
+static struct mtx_padalign ncneg_mtx;
+MTX_SYSINIT(vfscache_neg, &ncneg_mtx, "Name Cache neg", MTX_DEF);
+
/*
* UMA zones for the VFS cache.
*
@@ -436,12 +439,21 @@ SYSCTL_PROC(_debug_hashstat, OID_AUTO, n
* Negative entries management
*/
static void
-cache_negative_hit(struct namecache *ncp)
+cache_negative_hit(struct namecache *ncp, int wlocked)
{
- rw_assert(&cache_lock, RA_WLOCKED);
+ if (!wlocked) {
+ rw_assert(&cache_lock, RA_RLOCKED);
+ mtx_lock(&ncneg_mtx);
+ } else {
+ rw_assert(&cache_lock, RA_WLOCKED);
+ }
+
TAILQ_REMOVE(&ncneg, ncp, nc_dst);
TAILQ_INSERT_TAIL(&ncneg, ncp, nc_dst);
+
+ if (!wlocked)
+ mtx_unlock(&ncneg_mtx);
}
static void
@@ -680,16 +692,17 @@ negative_success:
return (0);
}
- if (!wlocked && !CACHE_UPGRADE_LOCK())
- goto wlock;
counter_u64_add(numneghits, 1);
- cache_negative_hit(ncp);
+ cache_negative_hit(ncp, wlocked);
if (ncp->nc_flag & NCF_WHITE)
cnp->cn_flags |= ISWHITEOUT;
SDT_PROBE2(vfs, namecache, lookup, hit__negative, dvp,
nc_get_name(ncp));
cache_out_ts(ncp, tsp, ticksp);
- CACHE_WUNLOCK();
+ if (wlocked)
+ CACHE_WUNLOCK();
+ else
+ CACHE_RUNLOCK();
return (ENOENT);
wlock:
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