lkml.org 
[lkml]   [2012]   [Jan]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH] Fix panic in __d_lookup with high dentry hashtable counts
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)


\
 
 \ /
  Last update: 2012-01-13 17:39    [W:0.052 / U:0.028 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site