linux-kernel - Re: [PATCH V2] x86/mm/pat: Do a small optimization and fix in reserve

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Date:	Tue, 21 Jul 2015 16:26:27 +0800
From:	Pan Xinhui <xinhuix.pan@...el.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	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 V2] x86/mm/pat: Do a small optimization and fix in reserve_memtype

hi, tglx
	thanks for your reply :)

On 2015年07月21日 16:10, Thomas Gleixner wrote:
> On Tue, 21 Jul 2015, Pan Xinhui wrote:
>> diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
>> index 188e3e0..f3c49fa 100644
>> --- a/arch/x86/mm/pat.c
>> +++ b/arch/x86/mm/pat.c
>> @@ -538,22 +538,20 @@ int reserve_memtype(u64 start, u64 end, enum page_cache_mode req_type,
>>  	new->type	= actual_type;
>>  
>>  	spin_lock(&memtype_lock);
>> -
>>  	err = rbt_memtype_check_insert(new, new_type);
>> +	actual_type = new->type;
> 
> What's the point of this? new->type is set to actual_type 5 lines above.
191 int rbt_memtype_check_insert(struct memtype *new,
192                  enum page_cache_mode *ret_type)
193 {
194     int err = 0;
195 
196     err = memtype_rb_check_conflict(&memtype_rbroot, new->start, new->end,
197                         new->type, ret_type);
198 
199     if (!err) {
200         if (ret_type)
201             new->type = *ret_type;
202 
So new->type might be set to *ret_type.

136     if (match->type != found_type && newtype == NULL)
137         goto failure;
138 
139     dprintk("Overlap at 0x%Lx-0x%Lx\n", match->start, match->end);
140     found_type = match->type;
141 
142     node = rb_next(&match->rb);
143     while (node) {
144         match = container_of(node, struct memtype, rb);
145 
146         if (match->start >= end) /* Checked all possible matches */
147             goto success;
148 
149         if (is_node_overlap(match, start, end) &&
150             match->type != found_type) {
151             goto failure;
152         }
153 
154         node = rb_next(&match->rb);
155     }
156 success:
157     if (newtype)
158         *newtype = found_type;

So *ret_type might be set to found_type(match->type),

The call train is deep, it took me long time to review them.
As actual_type != new->type is possible, we need save new->type to actual_type.

thanks
xinhui
> 
> Thanks,
> 
> 	tglx
> 
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