On Fri, Jan 13, 2012 at 04:22:36PM +0000, Al Viro wrote:
> On Fri, Jan 13, 2012 at 09:52:37AM -0600, Dimitri Sivanich wrote:
> > When the number of dentry cache hash table entries gets too high
> > (2147483648 entries), use of a signed integer in the initialization
> > loop prevents the dentry_hashtable from getting initialized, resulting
> > in a panic in __d_lookup. Fixing this in dcache_init and a few other
> > spots for consistency.
>
> > static void __init dcache_init(void)
> > {
> > - int loop;
> > + long loop;
>
> You've got to be kidding. Note that D_HASHMASK is at most 32bit. Use
> of long here is an overkill and so's 2^31 hash buckets (that's what,
> 16Gb in hash list heads alone? What kind of average chain length do
> you expect, BTW?)
Yes, long might be overkill right now, but the code is all __init time code.
I don't have numbers showing average chain length at this point, I was
simply fixing this one end case
>
> Can alloc_large_system_hash() produce the horrors that large, anyway?
On a 16TB system, alloc_large_system_hash() produces 2^31 hash buckets, yes.
Would simply capping the value in alloc_large_system_hash() be more palatable?
Something like the following?
Index: linux/mm/page_alloc.c
===================================================================
--- linux.orig/mm/page_alloc.c
+++ linux/mm/page_alloc.c
@@ -5257,6 +5257,7 @@ void *__init alloc_large_system_hash(con
if (max == 0) {
max = ((unsigned long long)nr_all_pages << PAGE_SHIFT) >> 4;
do_div(max, bucketsize);
+ max = min(max, 1ULL << 30);
}
if (numentries > max)
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