linux-kernel - Re: [PATCH] x86_32: trim memory by updating e820 v3

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Date:	Tue, 29 Apr 2008 12:44:07 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Gabriel C" <nix.or.die@...glemail.com>,
	"Andi Kleen" <andi@...stfloor.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Jesse Barnes" <jesse.barnes@...el.com>,
	"Mika Fischer" <mika.fischer@...pnet.de>, balajirrao@...il.com
Subject: Re: [PATCH] x86_32: trim memory by updating e820 v3

On Tue, Apr 29, 2008 at 12:19 PM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
> "Yinghai Lu" <yhlu.kernel@...il.com> writes:
>
>
> >>  The potential problem isn't while we reprogram the MTRRs, the potential
>  >>  problem is mapping the SMM area uncachable.  In which case we will
>  >>  make each SMM interrupt drastically slower.  Which can have all kinds of
>  >>  unpleasant side effects.
>  >
>  > and ACPI area too.
>
>  True but at least that one is visible.
>
>
>  > that only try to make the continuous to discrete layout. and still try
>  > to cover all that is (WBs - UC) directly with WB.
>  > only thing is that could run out of MTRR..., and mtrr_gran_size is
>  > used to avoid that.
>  > then some RAM that is less than mtrr_gran_size could be dumped.
>  > so mtrr_gran_size could do sth.
>  > anyway this patch only can meet one end.
>  > for example Mika Fischer's system doesn't need to trim any RAM in MTRR.
>  > but for Gabriel's system may need to trim some RAM in MTRR.
>
>  Right.  Ram trimming (changing memory from WB to UC) is the potential
>  problem.
>
>  See my other post, in short I think we can address safely address all
>  of the systems where the only problem is the selection of MTRRs by the
>  BIOS.

BIOS should provide the selection...

>
>  Then have an option (mtrr_chunk_size) for RAM trimming that is
>  off by default.

Yes. there is CONFIG option and boot command line to enable it.

YH
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