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

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Date:	Tue, 14 Jan 2014 15:02:29 +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 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.

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

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