linux-kernel - Re: [PATCH 3/3] zram: rework reported to end-user zram statistics

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Date:	Tue, 14 Jan 2014 15:20:55 +0100
From:	Jerome Marchand <jmarchan@...hat.com>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
CC:	Minchan Kim <minchan@...nel.org>, Nitin Gupta <ngupta@...are.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] zram: rework reported to end-user zram statistics

On 01/14/2014 03:09 PM, Sergey Senozhatsky wrote:
> On (01/14/14 15:02), Jerome Marchand wrote:
>> On 01/14/2014 02:53 PM, Sergey Senozhatsky wrote:
>>> On (01/14/14 14:43), Jerome Marchand wrote:
>>> [..]
>>>>>>
>>>>>> That's weird: good/bad_compress are accounted, but it seems to me that
>>>>>> they are to never used in any way. If so, there is indeed no reason to
>>>>>> keep them.
>>>>>>
>>>>>>
>>>>>>> Account each sub-request
>>>>>>> compression size so we can calculate real device compression ratio.
>>>>>>
>>>>>> Your patch doesn't change the way pages_stored and compr[essed]_size
>>>>>> are accounted. What does your patch change that allow us to calculate
>>>>>> the "real" compression ratio?
>>>>>>
>>>>>>>
>>>>>>> 4) reported zram stats:
>>>>>>>   - num_writes  -- number of writes
>>>>>>>   - num_reads  -- number of reads
>>>>>>>   - pages_stored -- number of pages currently stored
>>>>>>>   - compressed_size -- compressed size of pages stored
>>>>>>
>>>>>> Wouldn't it be more practical to report the original and compressed
>>>>>> data sizes using the same units as it is currently done?
>>>>>>
>>>>>
>>>>> hm, do we really need pages_stored stats? what kind of unseful information it
>>>>> shows to end user?.. perhaps, it's better to replace it with accounted passed
>>>>> bvec->bv_len (as uncompressed_size).
>>>>>
>>>>
>>>> That's really going to complicates things. We would need to keep track
>>>> of which sectors of a particular page has been written to. It's much
>>>> easier to keep current page granularity and consider any partial I/O
>>>> as an whole page I/O.
>>>>
>>>
>>> fair enough. thank you.
>>>
>>> 2/3 and 3/3 were changed according to your comments:
>>> - 2/3 drop READA check
>>> - 3/3 update commit message.
>>>
>>> ready to re-publish. may I add your ACK to all 3 patches or just to 1/3?
>>
>> The READA thing was my only concern for 2/3, so yes for this one.
>> Concerning the third patch, I'd like to see what other people think
>> about which stats we want to report.
>>
> 
> good. so I hold on for a bit to minimize the traffic and see what other
> people think. thank you.
> 
> 	-ss
> 
>>>>>
>>>>>> Jerome
>>>>>>
>>>>>>>   - pages_zero  -- number of zero filled pages
>>>>>>>   - failed_read -- number of failed reads
>>>>>>>   - failed_writes -- can happen when memory is too low
>>>>>>>   - invalid_io   -- non-page-aligned I/O requests
>>>>>>>   - notify_free  -- number of swap slot free notifications
>>>>>>>   - memory_used -- zs pool zs_get_total_size_bytes()

I also wonder if we should add size of meta-data to memory_used,
especially the table size which is probably not always negligible.

Jerome

>>>>>>>
>>>>>>> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
>>>>
>>>>
>>

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