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Subjecthash table sizes
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Hi,

On NUMA systems with way too much memory, the current algorithms for
determining the size of the inode and dentry hash tables ends up trying
to allocate tables that are so big they may not fit within the physical
memory of a single node. Ie. on a 256 node system with 512GB of RAM with
16KB pages it basically ends up eating up all the memory on node before
completing a boot because of this. The inode and dentry hashes are 256MB
each and the IP routing table hash is 128MB.

I have tried changing the algorithm as below and it seems to produce
reasonable results and almost identical numbers for the smaller /
mid-sized configs I looked at.

This is not meant to be a final patch, any input/oppinion is welcome.

Thanks,
Jes

--- orig/linux-2.6.0-test10/fs/dcache.c Sat Oct 25 11:42:58 2003
+++ linux-2.6.0-test10/fs/dcache.c Tue Nov 25 05:33:04 2003
@@ -1549,9 +1549,8 @@
static void __init dcache_init(unsigned long mempages)
{
struct hlist_head *d;
- unsigned long order;
unsigned int nr_hash;
- int i;
+ int i, order;

/*
* A constructor could be added for stable state like the lists,
@@ -1571,12 +1570,17 @@

set_shrinker(DEFAULT_SEEKS, shrink_dcache_memory);

+#if 0
#if PAGE_SHIFT < 13
mempages >>= (13 - PAGE_SHIFT);
#endif
mempages *= sizeof(struct hlist_head);
for (order = 0; ((1UL << order) << PAGE_SHIFT) < mempages; order++)
;
+#endif
+ mempages >>= (23 - (PAGE_SHIFT - 1));
+ order = max(2, fls(mempages));
+ order = min(12, order);

do {
unsigned long tmp;
@@ -1594,7 +1598,7 @@
__get_free_pages(GFP_ATOMIC, order);
} while (dentry_hashtable == NULL && --order >= 0);

- printk(KERN_INFO "Dentry cache hash table entries: %d (order: %ld, %ld bytes)\n",
+ printk(KERN_INFO "Dentry cache hash table entries: %d (order: %d, %ld bytes)\n",
nr_hash, order, (PAGE_SIZE << order));

if (!dentry_hashtable)
--- orig/linux-2.6.0-test10/fs/inode.c Sat Oct 25 11:44:53 2003
+++ linux-2.6.0-test10/fs/inode.c Tue Nov 25 05:33:27 2003
@@ -1333,17 +1333,21 @@
void __init inode_init(unsigned long mempages)
{
struct hlist_head *head;
- unsigned long order;
unsigned int nr_hash;
- int i;
+ int i, order;

for (i = 0; i < ARRAY_SIZE(i_wait_queue_heads); i++)
init_waitqueue_head(&i_wait_queue_heads[i].wqh);

+#if 0
mempages >>= (14 - PAGE_SHIFT);
mempages *= sizeof(struct hlist_head);
for (order = 0; ((1UL << order) << PAGE_SHIFT) < mempages; order++)
;
+#endif
+ mempages >>= (23 - (PAGE_SHIFT - 1));
+ order = max(2, fls(mempages));
+ order = min(12, order);

do {
unsigned long tmp;
-
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