afs: Increase vcache and dcache hash table sizes

Now that we are using a real hash function, larger hash tables
will be more useful.

The vcache hash tables are statically sized, and this increase will
add about a megabyte to the kernel module's memory footprint.

Update the algorithm used to dynamically size the dcache hash tables,
keeping the old behavior for small numbers of dcaches, but growing
the hash table's size to keep the average chain length near two
for a range of dcache numbers.  Cap the dcache hash tables at 32k
entries to avoid excessive resource usage.

This involves code from opr, namely opr/ffs.h, which is acceptable
in the kernel module because that header is a standalone header
like jhash.h, with no dependencies on the system.

Change-Id: I7cdb3e993b1c2ad177a46ecc06bfa2be52e619e5
Reviewed-on: http://gerrit.openafs.org/11679
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: Benjamin Kaduk <kaduk@mit.edu>

diff --git a/src/afs/afs.h b/src/afs/afs.h
index 2dc18fbc7dc12c8b89281f1eb79d3781338f371e..a9877d536d6f88665bba1c0f08e34d471943bd06 100644 (file)
--- a/src/afs/afs.h
+++ b/src/afs/afs.h
@@ -85,7 +85,7 @@ extern int afs_shuttingdown;
 #define        NSERVERS        16      /* hash table size for server table */
 #define        NVOLS           64      /* hash table size for volume table */
 #define        NFENTRIES       256     /* hash table size for disk volume table */
-#define VCSIZEBITS     10      /* log of stat cache hash table size */
+#define VCSIZEBITS     16      /* log of stat cache hash table size */
 #define        VCSIZE          (opr_jhash_size(VCSIZEBITS))
 #define CBRSIZE                512     /* call back returns hash table size */
 #define        PIGGYSIZE       1350    /* max piggyback size */

diff --git a/src/afs/afs_dcache.c b/src/afs/afs_dcache.c
index 56f883d18da02bebaf80e70f145382303ebe4892..1bb3bd33e85bd0f527be691ebc53cc852f9a4f05 100644 (file)
--- a/src/afs/afs_dcache.c
+++ b/src/afs/afs_dcache.c
@@ -20,6 +20,8 @@
 #include "afs/afs_cbqueue.h"
 #include "afs/afs_osidnlc.h"
 
+#include <opr/ffs.h>
+
 /* Forward declarations. */
 static void afs_GetDownD(int anumber, int *aneedSpace, afs_int32 buckethint);
 static int afs_FreeDiscardedDCache(void);
@@ -3249,6 +3251,7 @@ afs_dcacheInit(int afiles, int ablocks, int aDentries, int achunk, int aflags)
     struct dcache *tdp;
     int i;
     int code;
+    int afs_dhashbits;
 
     afs_freeDCList = NULLIDX;
     afs_discardDCList = NULLIDX;
@@ -3270,8 +3273,18 @@ afs_dcacheInit(int afiles, int ablocks, int aDentries, int achunk, int aflags)
     if (!aDentries)
        aDentries = DDSIZE;
 
+    /* afs_dhashsize defaults to 1024 */
     if (aDentries > 512)
        afs_dhashsize = 2048;
+    /* Try to keep the average chain length around two unless the table
+     * would be ridiculously big. */
+    if (aDentries > 4096) {
+       afs_dhashbits = opr_fls(aDentries) - 3;
+       /* Cap the hash tables to 32k entries. */
+       if (afs_dhashbits > 15)
+           afs_dhashbits = 15;
+       afs_dhashsize = opr_jhash_size(afs_dhashbits);
+    }
     /* initialize hash tables */
     afs_dvhashTbl = afs_osi_Alloc(afs_dhashsize * sizeof(afs_int32));
     osi_Assert(afs_dvhashTbl != NULL);