linux-kernel - Re: [RFC][PATCH 03/10] zsmalloc: introduce zs_can

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Date:	Thu, 4 Jun 2015 12:50:25 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 03/10] zsmalloc: introduce zs_can_compact() function

On Thu, Jun 04, 2015 at 12:42:30PM +0900, Sergey Senozhatsky wrote:
> On (06/04/15 12:30), Minchan Kim wrote:
> > > -- free objects in class: 5 (free-objs class capacity)
> > > -- page1: inuse 2
> > > -- page2: inuse 2
> > > -- page3: inuse 3
> > > -- page4: inuse 2
> > 
> > What scenario do you have a cocern?
> > Could you describe this example more clear?
> 
> you mean "how is this even possible"?

No I meant. I couldn't understand your terms. Sorry.

What free-objs class capacity is?
page1 is zspage?

Let's use consistent terms between us.

For example, maxobj-per-zspage is 4.
A is allocated and used. X is allocated but not used.
so we can draw a zspage below.

        AAXX

So we can draw several zspages linked list as below

AAXX - AXXX - AAAX

Could you describe your problem again?

Sorry.


> 
> well, for example,
> 
> make -jX
> make clean
> 
> can introduce a significant fragmentation. no new objects, just random
> objs removal. assuming that we keep some of the objects, allocated during
> compilation.
> 
> e.g.
> 
> ...
> 
> page1
>   allocate baz.so
>   allocate foo.o
> page2
>   allocate bar.o
>   allocate foo.so
> ...
> pageN
> 
> 
> 
> now `make clean`
> 
> page1:
>   allocated baz.so
>   empty
> 
> page2
>   empty
>   allocated foo.so
> 
> ...
> 
> pageN
> 
> in the worst case, every page can turn out to be ALMOST_EMPTY.
> 
> 	-ss

-- 
Kind regards,
Minchan Kim
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