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

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Date:	Tue, 14 Jan 2014 17:09:23 +0300
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Jerome Marchand <jmarchan@...hat.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 (01/14/14 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()
> >>>>>
> >>>>> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> >>
> >>
> 
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