Re: [LTP] [PATCH 2/2] readahead02: read in 2M chunks

[Madan <ma...@li...>]

On Tuesday 13 May 2014 12:25 PM, Jan Stancek wrote:
>
> ----- Original Message -----
>> From: "Madan" <ma...@li...>
>> To: ltp...@li...
>> Sent: Tuesday, 13 May, 2014 7:18:48 AM
>> Subject: Re: [LTP] [PATCH 2/2] readahead02: read in 2M chunks
>>
>>
>> On Tuesday 22 April 2014 02:07 PM, Jan Stancek wrote:
>>> Max readahead size has been limited since commit:
>>>     commit 6d2be915e589b58cb11418cbe1f22ff90732b6ac
>>>     Author: Raghavendra K T <rag...@li...>
>>>     Date:   Thu Apr 3 14:48:23 2014 -0700
>>>       mm/readahead.c: fix readahead failure for memoryless NUMA nodes
>>>                       and limit readahead pages
>>>
>>> Update testcase to read ahead in 2M chunks, this change is
>>> compatible with older kernels.
>>>
>>> Signed-off-by: Jan Stancek <jst...@re...>
>>> ---
>>>    testcases/kernel/syscalls/readahead/readahead02.c |    9 +++++++--
>>>    1 files changed, 7 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/testcases/kernel/syscalls/readahead/readahead02.c
>>> b/testcases/kernel/syscalls/readahead/readahead02.c
>>> index 8940821..5b1524e 100644
>>> --- a/testcases/kernel/syscalls/readahead/readahead02.c
>>> +++ b/testcases/kernel/syscalls/readahead/readahead02.c
>>> @@ -213,8 +213,13 @@ static void read_testfile(int do_readahead, const char
>>> *fname, size_t fsize,
>>>    		tst_brkm(TBROK | TERRNO, cleanup, "Failed to open %s", fname);
>>>
>>>    	if (do_readahead) {
>>> -		TEST(ltp_syscall(__NR_readahead, fd, (off64_t) 0,
>>> -			(size_t) fsize));
>>> +		/* read ahead in chunks, 2MB is maximum since 3.15-rc1 */
>>> +		for (i = 0; i < fsize; i += 2*1024*1024) {
>>> +			TEST(ltp_syscall(__NR_readahead, fd,
>>> +				(off64_t) i, 2*1024*1024));
>>> +			if (TEST_RETURN != 0)
>>> +				break;
>>> +		}
>>>    		check_ret(0);
>>>    		*cached = get_cached_size();
>>>
>> IMHO, This patch is not complete please also change the test pass
>> criteria what i have sent the patch for.
> Can you explain why?
>
> If test "reads ahead" (in 2M chunks) the same amount of data,
> why should pass criteria change?
>
> Regards,
> Jan
>
>>
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In my understanding, readahead can make a cache of upto 2M of cache 
pages in memory(i.e 512 and 32 pages in  x86 ,PPC64 respectively) ,, But 
earlier in this testcase we are looking for the cache value of half the 
size of the  read file. In my opinion cached_ra can hold max of 2M and 
not half the size of the reading file. well correct me if am wrong !!

Regards,
Madan