Re: [PATCH]mmap: add alignment for some variables

[Shaohua Li]

On Wed, 2011-03-30 at 09:06 +0800, Andrew Morton wrote:
> On Wed, 30 Mar 2011 09:01:22 +0800 Shaohua Li <shaohua.li@xxxxxxxxx> wrote:
> 
> > +/*
> > + * Make sure vm_committed_as in one cacheline and not cacheline shared with
> > + * other variables. It can be updated by several CPUs frequently.
> > + */
> > +struct percpu_counter vm_committed_as ____cacheline_internodealigned_in_smp;
> 
> The mystery deepens.  The only cross-cpu writeable fields in there are
> percpu_counter.lock and its companion percpu_counter.count.  If CPUs
> are contending for the lock then that itself is a problem - how does
> adding some padding to the struct help anything?
I had another patch trying to address the lock contention (for case
OVERCOMMIT_GUESS), will send out soon. But thought better to have the
correct alignment for OVERCOMMIT_NEVER case.

Thanks,
Shaohua

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