Re: [PATCH] guard mm->rss with page_table_lock (241p11)

[ebiederm@xmission.com (Eric W. Biederman)]

Mark Hahn <hahn@coffee.psychology.mcmaster.ca> writes:

> > > > +	spin_lock(&mm->page_table_lock);
> > > >  	mm->rss++;
> > > > +	spin_unlock(&mm->page_table_lock);
> > > >...
> > > 
> > > Would it not be better to use some sort of atomic add/subtract/clear
> operation
> 
> > > rather than a spinlock? (Which would also give you fewer atomic memory
> access
> 
> > > cycles).
> > 
> > This will unfortunately not do for all platforms. Please read
> > http://marc.theaimsgroup.com/?t=97630768100003&w=2&r=1 for the
> > last discussion of this.
> 
> which can be summarized as "yet another way sparc support screws Linux,
> and DMiller didn't want to fix his mess close to 2.4.0".  it's ridiculous
> for an inconsequential arch like sparc32 to cause fairly noticable problems
> for all other arches.
> 
> if noone beats me, I'll be submitting a patch to fix this silliness in 2.5.

The thing is we need a spinlock to actually change the page tables to
change the rss.  We pretty much get the accounting of rss under the
same spinlock for free.

Eric
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