linux-kernel - Re: [PATCH -v2] mm: frontswap: fix a wrong if condition in frontswap

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Message-ID: <50651CF5.5030903@oracle.com>
Date:	Fri, 28 Sep 2012 11:43:49 +0800
From:	Zhenzhong Duan <zhenzhong.duan@...cle.com>
To:	Paul Bolle <pebolle@...cali.nl>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Dan Magenheimer <dan.magenheimer@...cle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	levinsasha928@...il.com, Feng Jin <joe.jin@...cle.com>,
	dan.carpenter@...cle.com
Subject: Re: [PATCH -v2] mm: frontswap: fix a wrong if condition in frontswap_shrink



On 2012-09-27 19:35, Paul Bolle wrote:
> On Fri, 2012-09-21 at 16:40 +0800, Zhenzhong Duan wrote:
>>
>> @@ -275,7 +280,7 @@ static int __frontswap_shrink(unsigned long target_pages,
>>   	if (total_pages<= target_pages) {
>>   		/* Nothing to do */
>>   		*pages_to_unuse = 0;
>
> I think setting pages_to_unuse to zero here is not needed. It is
> initiated to zero in frontswap_shrink() and hasn't been touched since.
> See my patch at https://lkml.org/lkml/2012/9/27/250.
Yes, it's unneeded. But I didn't see warning as you said in above link 
when run 'make V=1 mm/frontswap.o'.
>> -		return 0;
>> +		return 1;
>>   	}
>>   	total_pages_to_unuse = total_pages - target_pages;
>>   	return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type);
>> @@ -302,7 +307,7 @@ void frontswap_shrink(unsigned long target_pages)
>>   	spin_lock(&swap_lock);
>>   	ret = __frontswap_shrink(target_pages,&pages_to_unuse,&type);
>>   	spin_unlock(&swap_lock);
>> -	if (ret == 0&&  pages_to_unuse)
>> +	if (ret == 0)
>>   		try_to_unuse(type, true, pages_to_unuse);
>>   	return;
>>   }
>
> Are you sure pages_to_unuse won't be zero here? I've stared quite a bit
> at __frontswap_unuse_pages() and it's not obvious pages_to_unuse (there
> also called unused) will never be zero when that function returns zero.
pages_to_unuse==0 means all pages need to be unused.

zduan

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