lkml.org 
[lkml]   [2002]   [Dec]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [patch] kmalloc_percpu -- 2 of 2
Hi Andrew,

On Wed, Dec 04, 2002 at 08:32:58PM -0800, Andrew Morton wrote:
> Where in the kernel is such a large number of 4-, 8- or 16-byte
> objects being used?

Well, kernel objects may not be that small, but one would expect
the per-cpu parts of the kernel objects to be sometimes small, often down to
a couple of counters counting statistics.

>
> The slab allocator will support caches right down to 1024 x 4-byte
> objects per page. Why is that not appropriate?

Well, if you allocated 4-byte objects directly from the slab allocator,
you aren't guranteed to *not* share a cache line with another object
modified by a different cpu.

>
> Sorry, but you have what is basically a brand new allocator in
> there, and we need a very good reason for including it. I'd like
> to know what that reason is, please.

The reason is concern about per-cpu allocation for small per-CPU
parts (typically counters) of objects. If a driver has two counters
counting reads and writes, you don't want to eat up a whole cacheline
for them for each CPU per instance of the device.

Thanks
--
Dipankar Sarma <dipankar@in.ibm.com> http://lse.sourceforge.net
Linux Technology Center, IBM Software Lab, Bangalore, India.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:31    [from the cache]
©2003-2011 Jasper Spaans. Advertise on this site