Re: Limit hash table size

Andrew Morton
2004-02-17T23:24:15Z

"Chen, Kenneth W" <kenneth.w.chen@intel.com> wrote:
>
> OK, here is another revision on top of what has been discussed. It adds
> 4 boot time parameters so user can override default size as needed to
> suite special needs.

You've set the default to 2M entries, with an option for this to be
increased via a boot parameter. This means that people whose machines have
lots of memory and a sane number of zones may suddenly wonder why their
app-which-uses-a-zillion-files is running like crap.

I think it would be better to leave things as they are, with a boot option
to scale the tables down. The below patch addresses the inode and dentry
caches. Need to think a bit more about the networking ones.

> I will sent a separate patch for
> kernel-parameters.txt if everyone is OK with this one.

Yes please.

diff -puN fs/dcache.c~limit-hash-table-sizes-boot-options-restore-defaults fs/dcache.c
--- 25/fs/dcache.c~limit-hash-table-sizes-boot-options-restore-defaults Tue Feb 17 15:11:09 2004
+++ 25-akpm/fs/dcache.c Tue Feb 17 15:11:29 2004
@@ -49,7 +49,6 @@ static kmem_cache_t *dentry_cache;
*/
#define D_HASHBITS d_hash_shift
#define D_HASHMASK d_hash_mask
-#define D_HASHMAX (2*1024*1024UL) /* max number of entries */

static unsigned int d_hash_mask;
static unsigned int d_hash_shift;
@@ -1567,12 +1566,11 @@ static void __init dcache_init(unsigned

set_shrinker(DEFAULT_SEEKS, shrink_dcache_memory);

- if (!dhash_entries) {
+ if (!dhash_entries)
dhash_entries = PAGE_SHIFT < 13 ?
mempages >> (13 - PAGE_SHIFT) :
mempages << (PAGE_SHIFT - 13);
- dhash_entries = min(D_HASHMAX, dhash_entries);
- }
+
dhash_entries *= sizeof(struct hlist_head);
for (order = 0; ((1UL << order) << PAGE_SHIFT) < dhash_entries; order++)
;
diff -puN fs/inode.c~limit-hash-table-sizes-boot-options-restore-defaults fs/inode.c
--- 25/fs/inode.c~limit-hash-table-sizes-boot-options-restore-defaults Tue Feb 17 15:11:09 2004
+++ 25-akpm/fs/inode.c Tue Feb 17 15:11:47 2004
@@ -53,7 +53,6 @@
*/
#define I_HASHBITS i_hash_shift
#define I_HASHMASK i_hash_mask
-#define I_HASHMAX (2*1024*1024UL) /* max number of entries */

static unsigned int i_hash_mask;
static unsigned int i_hash_shift;
@@ -1336,12 +1335,11 @@ void __init inode_init(unsigned long mem
for (i = 0; i < ARRAY_SIZE(i_wait_queue_heads); i++)
init_waitqueue_head(&i_wait_queue_heads[i].wqh);

- if (!ihash_entries) {
+ if (!ihash_entries)
ihash_entries = PAGE_SHIFT < 14 ?
mempages >> (14 - PAGE_SHIFT) :
mempages << (PAGE_SHIFT - 14);
- ihash_entries = min(I_HASHMAX, ihash_entries);
- }
+
ihash_entries *= sizeof(struct hlist_head);
for (order = 0; ((1UL << order) << PAGE_SHIFT) < ihash_entries; order++)
;