Re: [PATCH 1/3] proc: add /proc/kpageorder interface

[Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>]

On Monday 04 June 2012 21:31:25 KOSAKI Motohiro wrote:
> (6/4/12 4:23 AM), Bartlomiej Zolnierkiewicz wrote:
> > On Friday 01 June 2012 22:31:01 KOSAKI Motohiro wrote:
> >> (6/1/12 12:54 PM), Bartlomiej Zolnierkiewicz wrote:
> >>> From: Bartlomiej Zolnierkiewicz<b.zolnierkie@samsung.com>
> >>> Subject: [PATCH] proc: add /proc/kpageorder interface
> >>>
> >>> This makes page order information available to the user-space.
> >>
> >> No usecase new feature always should be NAKed.
> >
> > It is used to get page orders for Buddy pages and help to monitor
> > free/used pages.  Sample usage will be posted for inclusion to
> > Pagemap Demo tools (http://selenic.com/repo/pagemap/).
> >
> > The similar situation is with /proc/kpagetype..
> 
> NAK then.
> 
> First, your explanation didn't describe any usecase. "There is a similar feature"
> is NOT a usecase.
> 
> Second, /proc/kpagetype is one of mistaken feature. It was not designed deeply.
> We have no reason to follow the mistake.

Well, my usecase for /proc/kpagetype is to monitor/debug pageblock changes
(i.e. to verify CMA and compaction operations).  It is not perfect since
interface gives us only a snapshot of pageblocks state at some random time.
However it is a straightforward method and requires only minimal changes
to the existing code.

Maybe there is a better way to do this which would give a more accurate
data and capture every state change (maybe a one involving tracing?) but
I don't know about it.  Do you know such better way to do it?

> Third, pagemap demo doesn't describe YOUR feature's usefull at all.

pagemap demo doesn't include my patches for /proc/kpage[order,type] yet
so it is not surprising at all (it doesn't even work with current kernels
without my other patches).. ;)

> Fourth, pagemap demo is NOT useful at all. It's just toy. Practically, kpagetype
> is only used from pagetype tool.

I don't quite follow it, what pagetype tool are you referring to (kpagetype
is a new interface)?

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung Poland R&D Center

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