lkml.org 
[lkml]   [2008]   [May]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [patch 21/21] slab defrag: Obsolete SLAB
From
Date

On Thu, 2008-05-15 at 10:05 -0700, Christoph Lameter wrote:
> On Thu, 15 May 2008, Zhang, Yanmin wrote:
>
> > > It can thrash cachelines if objects from the same slab page are freed
> > > simultaneously on multiple processors. That occurred in the hackbench
> > > regression that we addressed with the dynamic configuration of slab sizes.
> > hackbench regression is because of slow allocation instead of slow freeing.
> > With ÿÿdynamic configuration of slab sizes, fast allocation becomes 97% (the bad
> > one is 68%), but fast free is always 8~9% with/without the patch.
>
> Thanks for using the slab statistics. I wish I had these numbers for the
> TPC benchmark. That would allow us to understand what is going on while it
> is running.
>
> The frees in the hackbench were slow because partial list updates occurred
> to frequently. The first fix was to let slab sit longer on the partial
> list.
I forgot that. 2.6.24 merged the patch.

> The other was the increase of the slab sizes which also increases
> the per cpu slab size and therefore the objects allocatable without a
> round trip to the page allocator.
That is what I am talking. 2.6.26-rc merged the patch.

> Freeing to a per cpu slab never requires
> partial list updates. So the frees also benefitted from the larger slab
> sizes. But the effect shows up in the count of partial list updates not in
> the fast/free collumn.
I agree. It might be better if SLUB could be optimized again to have more consideration
when the slow free percentage is high, because the page lock might ping-pong
among processors if multi-processors access the same slab at the same time.

--
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: 2008-05-16 07:21    [W:0.136 / U:0.456 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site