linux-kernel - Re: [PATCH 1/2] x86/fpu, fork: Dynamically allocate 'struct fpu'

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Message-ID: <20150717192348.GB24300@gmail.com>
Date:	Fri, 17 Jul 2015 21:23:48 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	linux-kernel@...r.kernel.org, Dave Hansen <dave@...1.net>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave@...1.net>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Brian Gerst <brgerst@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/2] x86/fpu, fork: Dynamically allocate 'struct fpu'


* Ingo Molnar <mingo@...nel.org> wrote:

> From: Dave Hansen <dave@...1.net>
> 
> The FPU rewrite removed the dynamic allocations of 'struct fpu'.
> But, this potentially wastes massive amounts of memory (2k per
> task on systems that do not have AVX-512 for instance).
> 
> Instead of having a separate slab, this patch just appends the
> space that we need to the 'task_struct' which we dynamically
> allocate already.  This saves from doing an extra slab
> allocation at fork().
> 
> The only real downside here is that we have to stick everything
> and the end of the task_struct.  But, I think the BUILD_BUG_ON()s
> I stuck in there should keep that from being too fragile.
> 
> Cc: Andy Lutomirski <luto@...capital.net>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: dave@...1.net
> Link: http://lkml.kernel.org/r/20150716191437.A334FF2E@viggo.jf.intel.com
> Signed-off-by: Ingo Molnar <mingo@...nel.org>

Dave, can I put your Signed-off-by into this patch? I have already tested these 
two patches and they are looking good here - so unless you can see some breakage 
or other problem I'd prefer it to keep it two patches.

Thanks,

	Ingo
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