linux-kernel - Re: [PATCH] z3fold: the 3-fold allocator for compressed pages

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Date:	Thu, 14 Apr 2016 13:13:01 +0200
From:	Vitaly Wool <vitalywool@...il.com>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	Seth Jennings <sjenning@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Streetman <ddstreet@...e.org>
Subject: Re: [PATCH] z3fold: the 3-fold allocator for compressed pages

[resending due to mail client issues]

On Thu, Apr 14, 2016 at 10:48 AM, Vlastimil Babka <vbabka@...e.cz> wrote:
>
> On 04/14/2016 10:05 AM, Vitaly Wool wrote:
>>
>> This patch introduces z3fold, a special purpose allocator for storing
>> compressed pages. It is designed to store up to three compressed pages per
>> physical page. It is a ZBUD derivative which allows for higher compression
>> ratio keeping the simplicity and determinism of its predecessor.
>
>
> So the obvious question is, why a separate allocator and not extend zbud?

Well, as far as I recall Seth was very much for keeping zbud as simple
as possible. I am fine either way but if we have zpool API, why not
have another zpool API user?

>
> I didn't study the code, nor notice a design/algorithm overview doc, but it seems z3fold keeps the idea of one compressed page at the beginning, one at the end of page frame, but it adds another one in the middle? Also how is the buddy-matching done?


Basically yes. There is 'start_middle' variable which point to the
start of the middle page, if any. The matching is done basing on the
buddy number.

~vitaly