linux-kernel - Re: [RFC][PATCH v2 3/3] mm/zsmalloc: increase ZS_MAX_PAGES_PER

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Message-ID: <20160222023432.GC27829@bbox>
Date:	Mon, 22 Feb 2016 11:34:32 +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>,
	Joonsoo Kim <js1304@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH v2 3/3] mm/zsmalloc: increase ZS_MAX_PAGES_PER_ZSPAGE

On Mon, Feb 22, 2016 at 11:01:13AM +0900, Sergey Senozhatsky wrote:
> On (02/22/16 10:34), Minchan Kim wrote:
> [..]
> > > > I tempted it several times with same reason you pointed out.
> > > > But my worry was that if we increase ZS_MAX_ZSPAGE_ORDER, zram can
> > > > consume more memory because we need several pages chain to populate
> > > > just a object. Even, at that time, we didn't have compaction scheme
> > > > so fragmentation of object in zspage is huge pain to waste memory.
> > > 
> > > well, the thing is -- we end up requesting less pages after all, so
> > > zsmalloc has better chances to survive. for example, gcc5 compilation test
> > 
> > Indeed. I saw your test result.
> 
> 
> [..]
> > >  Total               129          489       1627756    1618193     850147
> > > 
> > > 
> > > that's  891703 - 850147 = 41556 less pages. or 162MB less memory used.
> > > 41556 less pages means that zsmalloc had 41556 less chances to fail.
> > 
> > 
> > Let's think swap-case which is more important for zram now. As you know,
> > most of usecase are swap in embedded world.
> > Do we really need 16 pages allocator for just less PAGE_SIZE objet
> > at the moment which is really heavy memory pressure?
> 
> I'll take a look at dynamic class page addition.

Thanks, Sergey.

Just a note:

I am preparing zsmalloc migration now and almost done so I hope
I can send it within two weeks. In there, I changed a lot of
things in zsmalloc, page chaining, struct page fields usecases
and locking scheme and so on. The zsmalloc fragment/migration
is really painful now so we should solve it first so I hope
you help to review that and let's go further dynamic chaining
after that, please. :)