linux-kernel - Re: [Approach #2] [RFC][PATCH] Remove cgroup member from struct page

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Date:	Wed, 10 Sep 2008 15:56:48 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	kamezawa.hiroyu@...fujitsu.com,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>, hugh@...itas.com,
	menage@...gle.com, xemul@...nvz.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [Approach #2] [RFC][PATCH] Remove cgroup member from struct
	page

On Wed, 2008-09-10 at 15:36 -0700, Balbir Singh wrote:
> Dave Hansen wrote:
> > On Tue, 2008-09-09 at 18:20 -0700, Balbir Singh wrote:
> >> +       start = pgdat->node_start_pfn;
> >> +       end = pgdat->node_start_pfn + pgdat->node_spanned_pages;
> >> +       size = (end - start) * sizeof(struct page_cgroup);
> >> +       printk("Allocating %lu bytes for node %d\n", size, n);
> >> +       pcg_map[n] = alloc_bootmem_node(pgdat, size);
> >> +       /*
> >> +        * We can do smoother recovery
> >> +        */
> >> +       BUG_ON(!pcg_map[n]);
> >> +       return 0;
> >>  }
> > 
> > This will really suck for sparse memory machines.  Imagine a machine
> > with 1GB of memory at 0x0 and another 1GB of memory at 1TB up in the
> > address space.
> > 
> 
> I would hate to re-implement the entire sparsemem code :(
> Kame did suggest making the memory controller depend on sparsemem (to hook in
> from there for allocations)

Yeah, you could just make another mem_section member.  Or, you could
work to abstract the sparsemem code so that other people can use it, or
maybe make it more dynamic so we can have multiple pfn->object lookups
in parallel.  Adding the struct member is obviously easier.

-- Dave

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