linux-kernel - Re: [RFC 8/8] Reduce inode memory usage for systems with a high MAX

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Date:	Tue, 16 Jan 2007 12:06:50 -0800
From:	"Paul Menage" <menage@...gle.com>
To:	"Christoph Lameter" <clameter@....com>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org,
	"Nick Piggin" <nickpiggin@...oo.com.au>, linux-mm@...ck.org,
	"Andi Kleen" <ak@...e.de>, "Paul Jackson" <pj@....com>,
	"Dave Chinner" <dgc@....com>
Subject: Re: [RFC 8/8] Reduce inode memory usage for systems with a high MAX_NUMNODES

On 1/16/07, Christoph Lameter <clameter@....com> wrote:
> On Tue, 16 Jan 2007, Paul Menage wrote:
>
> > On 1/15/07, Christoph Lameter <clameter@....com> wrote:
> > >
> > > This solution may be a bit hokey. I tried other approaches but this
> > > one seemed to be the simplest with the least complications. Maybe someone
> > > else can come up with a better solution?
> >
> > How about a 64-bit field in struct inode that's used as a bitmask if
> > there are no more than 64 nodes, and a pointer to a bitmask if there
> > are more than 64 nodes. The filesystems wouldn't need to be involved
> > then, as the bitmap allocation could be done in the generic code.
>
> How would we decide if there are more than 64 nodes? Runtime or compile
> time?

I was thinking runtime, unless MAX_NUMNODES is less than 64 in which
case you can make the decision at compile time.

>
> If done at compile time then we will end up with a pointer to an unsigned
> long for a system with <= 64 nodes. If we allocate the nodemask via
> kmalloc then we will always end up with a mininum allocation size of 64
> bytes.

Can't we get less overhead with a slab cache with appropriate-sized objects?

Paul
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