Re: Limit hash table size

[Manfred Spraul <manfred@colorfullife.com>]

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>
>
>Why cant we do something like Andrews recent min_free_kbytes patch and
>make the rate of change non linear. Just slow the increase down as we
>get bigger. I agree a 2GB hashtable is pretty ludicrous, but a 4MB one
>on a 512GB machine (which we sell at the moment) could be too :)
>  
>
What about making the limit configurable with a boot time parameter? If 
someone uses a 512 GB ppc64 as an nfs server, he might want a 2 GB inode 
hash.

--
    Manfred

[-- Attachment #2: patch-hash-alloc --]
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// $Header$
// Kernel Version:
//  VERSION = 2
//  PATCHLEVEL = 6
//  SUBLEVEL = 0
//  EXTRAVERSION = -test11
--- 2.6/fs/inode.c	2003-11-29 09:46:34.000000000 +0100
+++ build-2.6/fs/inode.c	2003-11-29 10:19:21.000000000 +0100
@@ -1327,6 +1327,20 @@
 		wake_up_all(wq);
 }
 
+static __initdata int ihash_entries;
+
+static int __init set_ihash_entries(char *str)
+{
+	get_option(&str, &ihash_entries);
+	if (ihash_entries <= 0) {
+		ihash_entries = 0;
+		return 0;
+	}
+	return 1;
+}
+
+__setup("ihash_entries=", set_ihash_entries);
+
 /*
  * Initialize the waitqueues and inode hash table.
  */
@@ -1340,8 +1354,16 @@
 	for (i = 0; i < ARRAY_SIZE(i_wait_queue_heads); i++)
 		init_waitqueue_head(&i_wait_queue_heads[i].wqh);
 
-	mempages >>= (14 - PAGE_SHIFT);
-	mempages *= sizeof(struct hlist_head);
+	if (!ihash_entries) {
+		ihash_entries = mempages >> (14 - PAGE_SHIFT);
+		/* Limit inode hash size. Override for nfs servers
+		 * that handle lots of files.
+		 */
+		if (ihash_entries > 1024*1024)
+			ihash_entries = 1024*1024;
+	}
+
+	mempages = ihash_entries*sizeof(struct hlist_head);
 	for (order = 0; ((1UL << order) << PAGE_SHIFT) < mempages; order++)
 		;
 
--- 2.6/fs/dcache.c	2003-11-29 09:46:34.000000000 +0100
+++ build-2.6/fs/dcache.c	2003-11-29 10:53:15.000000000 +0100
@@ -1546,6 +1546,20 @@
 	return ino;
 }
 
+static __initdata int dhash_entries;
+
+static int __init set_dhash_entries(char *str)
+{
+	get_option(&str, &dhash_entries);
+	if (dhash_entries <= 0) {
+		dhash_entries = 0;
+		return 0;
+	}
+	return 1;
+}
+
+__setup("dhash_entries=", set_dhash_entries);
+
 static void __init dcache_init(unsigned long mempages)
 {
 	struct hlist_head *d;
@@ -1571,10 +1585,18 @@
 	
 	set_shrinker(DEFAULT_SEEKS, shrink_dcache_memory);
 
+	if (!dhash_entries) {
 #if PAGE_SHIFT < 13
-	mempages >>= (13 - PAGE_SHIFT);
+		mempages >>= (13 - PAGE_SHIFT);
 #endif
-	mempages *= sizeof(struct hlist_head);
+		dhash_entries = mempages;
+		/* 8 mio is enough for general purpose systems.
+		 * For file servers, override with "dhash_entries="
+		 */
+		if (dhash_entries > 8*1024*1024)
+			dhash_entries = 8*1024*1024;
+	}
+	mempages = dhash_entries*sizeof(struct hlist_head);
 	for (order = 0; ((1UL << order) << PAGE_SHIFT) < mempages; order++)
 		;