linux-kernel - Re: Commit 34d76c41 causes linker errors on ia64 with NR

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Message-ID: <alpine.LRH.2.00.0910200356340.20992@twin.jikos.cz>
Date:	Tue, 20 Oct 2009 04:02:14 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Jeff Mahoney <jeffm@...e.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Tony Luck <tony.luck@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>, linux-ia64@...r.kernel.org
Subject: Re: Commit 34d76c41 causes linker errors on ia64 with NR_CPUS=4096

On Sun, 18 Oct 2009, Jeff Mahoney wrote:

> Hi Peter -
> 
> Commit 34d76c41 introduced the update_shares_data percpu, but it ends up
> causing problems on large ia64 machines. Specifically, ia64 is limited
> to 64k in percpu vars and with NR_CPUS=4096, that ends up being 32k by
> itself. It ends up causing link errors since that is how ia64 enforces
> the 64k limit.
> 
> I can take a deeper look at finding a workable solution but thought I'd
> mention it in case you had ideas already.

I am adding some IA64 CCs, as the failure is solely caused by the ia64 
percpu implementation/pagefault handler optimization which requires the 
.percpu section area not be larger than 64k, which blows up with 34d76c41 
and NR_CPUS high enoufh (due to introduction of percpu array being 
size-dependent on NR_CPUS).

-- 
Jiri Kosina
SUSE Labs, Novell Inc.

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