Re: [PATCH 4/4] zcache: add pageframes count once compress zero-filled pages twice

[Wanpeng Li <liwanp@linux.vnet.ibm.com>]

On Wed, Mar 13, 2013 at 09:42:16AM -0700, Dan Magenheimer wrote:
>> From: Wanpeng Li [mailto:liwanp@linux.vnet.ibm.com]
>> Sent: Wednesday, March 13, 2013 1:05 AM
>> To: Andrew Morton
>> Cc: Greg Kroah-Hartman; Dan Magenheimer; Seth Jennings; Konrad Rzeszutek Wilk; Minchan Kim; linux-
>> mm@kvack.org; linux-kernel@vger.kernel.org; Wanpeng Li
>> Subject: [PATCH 4/4] zcache: add pageframes count once compress zero-filled pages twice
>
>Hi Wanpeng --
>
>Thanks for taking on this task from the drivers/staging/zcache TODO list!
>
>> Since zbudpage consist of two zpages, two zero-filled pages compression
>> contribute to one [eph|pers]pageframe count accumulated.
>

Hi Dan,

>I'm not sure why this is necessary.  The [eph|pers]pageframe count
>is supposed to be counting actual pageframes used by zcache.  Since
>your patch eliminates the need to store zero pages, no pageframes
>are needed at all to store zero pages, so it's not necessary
>to increment zcache_[eph|pers]_pageframes when storing zero
>pages.
>

Great point! It seems that we also don't need to caculate 
zcache_[eph|pers]_zpages for zero-filled pages. I will fix 
it in next version. :-)

>Or am I misunderstanding your intent?
>

Regards,
Wanpeng Li 

>Thanks,
>Dan
> 
>> Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
>> ---
>>  drivers/staging/zcache/zcache-main.c |   25 +++++++++++++++++++++++--
>>  1 files changed, 23 insertions(+), 2 deletions(-)
>> 
>> diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c
>> index dd52975..7860ff0 100644
>> --- a/drivers/staging/zcache/zcache-main.c
>> +++ b/drivers/staging/zcache/zcache-main.c
>> @@ -544,6 +544,8 @@ static struct page *zcache_evict_eph_pageframe(void);
>>  static void *zcache_pampd_eph_create(char *data, size_t size, bool raw,
>>  					struct tmem_handle *th)
>>  {
>> +	static ssize_t second_eph_zero_page;
>> +	static atomic_t second_eph_zero_page_atomic = ATOMIC_INIT(0);
>>  	void *pampd = NULL, *cdata = data;
>>  	unsigned clen = size;
>>  	bool zero_filled = false;
>> @@ -561,7 +563,14 @@ static void *zcache_pampd_eph_create(char *data, size_t size, bool raw,
>>  		clen = 0;
>>  		zero_filled = true;
>>  		zcache_pages_zero++;
>> -		goto got_pampd;
>> +		second_eph_zero_page = atomic_inc_return(
>> +				&second_eph_zero_page_atomic);
>> +		if (second_eph_zero_page % 2 == 1)
>> +			goto got_pampd;
>> +		else {
>> +			atomic_sub(2, &second_eph_zero_page_atomic);
>> +			goto count_zero_page;
>> +		}
>>  	}
>>  	kunmap_atomic(user_mem);
>> 
>> @@ -597,6 +606,7 @@ static void *zcache_pampd_eph_create(char *data, size_t size, bool raw,
>>  create_in_new_page:
>>  	pampd = (void *)zbud_create_prep(th, true, cdata, clen, newpage);
>>  	BUG_ON(pampd == NULL);
>> +count_zero_page:
>>  	zcache_eph_pageframes =
>>  		atomic_inc_return(&zcache_eph_pageframes_atomic);
>>  	if (zcache_eph_pageframes > zcache_eph_pageframes_max)
>> @@ -621,6 +631,8 @@ out:
>>  static void *zcache_pampd_pers_create(char *data, size_t size, bool raw,
>>  					struct tmem_handle *th)
>>  {
>> +	static ssize_t second_pers_zero_page;
>> +	static atomic_t second_pers_zero_page_atomic = ATOMIC_INIT(0);
>>  	void *pampd = NULL, *cdata = data;
>>  	unsigned clen = size, zero_filled = 0;
>>  	struct page *page = (struct page *)(data), *newpage;
>> @@ -644,7 +656,15 @@ static void *zcache_pampd_pers_create(char *data, size_t size, bool raw,
>>  		clen = 0;
>>  		zero_filled = 1;
>>  		zcache_pages_zero++;
>> -		goto got_pampd;
>> +		second_pers_zero_page = atomic_inc_return(
>> +				&second_pers_zero_page_atomic);
>> +		if (second_pers_zero_page % 2 == 1)
>> +			goto got_pampd;
>> +		else {
>> +			atomic_sub(2, &second_pers_zero_page_atomic);
>> +			goto count_zero_page;
>> +		}
>> +
>>  	}
>>  	kunmap_atomic(user_mem);
>> 
>> @@ -698,6 +718,7 @@ create_pampd:
>>  create_in_new_page:
>>  	pampd = (void *)zbud_create_prep(th, false, cdata, clen, newpage);
>>  	BUG_ON(pampd == NULL);
>> +count_zero_page:
>>  	zcache_pers_pageframes =
>>  		atomic_inc_return(&zcache_pers_pageframes_atomic);
>>  	if (zcache_pers_pageframes > zcache_pers_pageframes_max)
>> --
>> 1.7.7.6

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