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

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Message-Id: <20080911105638.1581db90.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 11 Sep 2008 10:56:38 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	Dave Hansen <dave@...ux.vnet.ibm.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, 10 Sep 2008 18:47:25 -0700
Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:

> KAMEZAWA Hiroyuki wrote:
> > On Wed, 10 Sep 2008 15:56:48 -0700
> > Dave Hansen <dave@...ux.vnet.ibm.com> wrote:
> > 
> >> 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.
> >>
> > Don't worry. I'll care sparse memory map and hotplug.
> > But whether making this depends on SPARSEMEM or not is not fixed yet.
> > I'll try generic one, at first. If it's dirty, start discussion about SPARSEMEM.
> > 
> > (Honestly, I love sparsemem than others ;)
> 
> My concern is that if we depend on sparsemem, then we force distros to turn on
> sparsemem (which might be the default, but not on all architectures), we might
> end up losing those architectures (w.r.t. turning on the memory controller)
> where sparsemem is not the default on the distro.
> 
Yes. I share your concern. Then, I'll try not-on-sparsemem version, at first.

Thanks,
-Kame

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