Re: Limit hash table size

Manfred Spraul
2004-01-12T16:50:55Z

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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++)
;