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 20:54:30 +0800
From:	Pan Xinhui <xinhuix.pan@...el.com>
To:	Borislav Petkov <bp@...en8.de>
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

hi, Borislav
	thanks for your reply. :)

On 2015年07月22日 18:46, Borislav Petkov wrote:
> 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."
> 
thanks!

>> 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()
agree, output all debugging information.

> call should dump actual_type and req_type because this way we show what
then why not append "act %s" to the dprintk format string?

> 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.
yes, new->type is same with *new_type, and dump same value twice.

> 
> Ok?
> 
Let me think for a while. I wonder why there is not any comment that could tell developers what "track %s" mean.
In different places of this file, "track %s" can mean what type of memory it is now, or it used to be.

So I think this output filed "track %s" is just whatever people want to need to print out.

I prefer to dump all debugging information here, so I agree with your idea. thanks

> 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);
> 
seems better now, thanks!
> while at it.
> 
> Thanks.
> 

thanks
xinhui
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