Re: [PATCH 0/3] Allow ZRAM to use any zpool-compatible backend

From: Vitaly Wool <vitalywool@gmail.com>
To: Minchan Kim <minchan@kernel.org>
Cc: Linux-MM <linux-mm@kvack.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	 Dan Streetman <ddstreet@ieee.org>,
	Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	 LKML <linux-kernel@vger.kernel.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	 Shakeel Butt <shakeelb@google.com>,
	Henry Burns <henrywolfeburns@gmail.com>,
	 "Theodore Ts'o" <tytso@thunk.org>
Subject: Re: [PATCH 0/3] Allow ZRAM to use any zpool-compatible backend
Date: Mon, 14 Oct 2019 18:50:22 +0200	[thread overview]
Message-ID: <CAMJBoFNuu+-Xu8j5xPyqHHMNfhT8t_2kXef_HRMQcT=WCTBCFw@mail.gmail.com> (raw)
In-Reply-To: <20191014164110.GA58307@google.com>

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Den mån 14 okt. 2019 18:41Minchan Kim <minchan@kernel.org> skrev:

> On Thu, Oct 10, 2019 at 11:04:14PM +0300, Vitaly Wool wrote:
> > The coming patchset is a new take on the old issue: ZRAM can currently
> be used only with zsmalloc even though this may not be the optimal
> combination for some configurations. The previous (unsuccessful) attempt
> dates back to 2015 [1] and is notable for the heated discussions it has
> caused.
> >
> > The patchset in [1] had basically the only goal of enabling ZRAM/zbud
> combo which had a very narrow use case. Things have changed substantially
> since then, and now, with z3fold used widely as a zswap backend, I, as the
> z3fold maintainer, am getting requests to re-interate on making it possible
> to use ZRAM with any zpool-compatible backend, first of all z3fold.
> >
> > The preliminary results for this work have been delivered at Linux
> Plumbers this year [2]. The talk at LPC, though having attracted limited
> interest, ended in a consensus to continue the work and pursue the goal of
> decoupling ZRAM from zsmalloc.
> >
> > The current patchset has been stress tested on arm64 and x86_64 devices,
> including the Dell laptop I'm writing this message on now, not to mention
> several QEmu confugirations.
> >
> > [1] https://lkml.org/lkml/2015/9/14/356
> > [2] https://linuxplumbersconf.org/event/4/contributions/551/
>
> Please describe what's the usecase in real world, what's the benefit
> zsmalloc
> cannot fulfill by desgin and how it's significant.
> I really don't want to make fragmentaion of allocator so we should really
> see
> how zsmalloc cannot achieve things if you are claiming.
> Please tell us how to test it so that we could investigate what's the root
> cause.
>

Fragmentation? What do you mean by that?

~Vitaly

>

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