Re: [RFC][PATCH 03/10] zsmalloc: introduce zs_can_compact() function

Minchan Kim
2015-06-04T03:50:38Z

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