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

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Message-ID: <20160222020113.GB488@swordfish>
Date:	Mon, 22 Feb 2016 11:01:13 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	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 (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.

	-ss