linux-kernel - Re: [PATCH V3] x86/mm/pat: Do a small optimization and fix in reserve

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Date:	Wed, 22 Jul 2015 12:46:24 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Pan Xinhui <xinhuix.pan@...el.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>, mingo@...hat.com,
	hpa@...or.com, x86@...nel.org, bp@...e.de, toshi.kani@...com,
	jgross@...e.com, mcgrof@...e.com,
	"mnipxh@....com" <mnipxh@....com>,
	"yanmin_zhang@...ux.intel.com" <yanmin_zhang@...ux.intel.com>
Subject: Re: [PATCH V3] x86/mm/pat: Do a small optimization and fix in
 reserve_memtype

On Wed, Jul 22, 2015 at 05:06:04PM +0800, Pan Xinhui wrote:
> how about:
> memtype_lock protects the rb-tree root and the rb-nodes which is a field of memtype from delete/add/lookup in a race.

Use this:

"All pat_rbtree operations need to be performed while holding the
memtype_lock."

> Actually I have same questions. I find these output logs are added in
> commit: 6997ab4982a29925e79f72c3a59823cf944c3529(x86: add PAT related
> debug prints) In the past, *new_type == actual_type == new->type on
> success. codes are below. author use actual_type there.

So this function is one bit PITA. So req_type is used to compute actual
type a bit higher:

	actual_type = pat_x_mtrr_type(start, end, req_type);

and from then on actual_type is being used.

BUT!, in order to have *all* debugging information, the last dprintk()
call should dump actual_type and req_type because this way we show what
pat_x_mtrr_type() did too. And we don't need to dump new->type because
this is the !err case and in that case we assigned new_type to it, which
we dump already.

Ok?

Btw, you could also simplify this:

	if (is_range_ram == 1) {

		err = reserve_ram_pages_type(start, end, req_type, new_type);

		return err;
	}

to:

	if (is_range_ram == 1)
		return reserve_ram_pages_type(start, end, req_type, new_type);

while at it.

Thanks.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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