linux-kernel - Re: [PATCH v1 0/7] writeback incompressible pages to storage

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Date:   Thu, 29 Jun 2017 18:17:13 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Juneho Choi <juno.choi@....com>,
        kernel-team <kernel-team@....com>
Subject: Re: [PATCH v1 0/7] writeback incompressible pages to storage

Hello,

On (06/29/17 17:47), Minchan Kim wrote:
[..]
> > > This patch supports writeback feature of zram so admin can set up
> > > a block device and with it, zram can save the memory via writing
> > > out the incompressile pages once it found it's incompressible pages
> > > (1/4 comp ratio) instead of keeping the page in memory.
> > 
> > hm, alternative idea. just an idea. can we try compressing the page
> > with another algorithm? example: downcast from lz4 to zlib? we can
> > set up a fallback "worst case" algorithm, so each entry can contain
> > additional flag that would tell if the src page was compressed with
> > the fast or slow algorithm. that sounds to me easier than "create a
> > new block device and bond it to zram, etc". but I may be wrong.
> 
> We tried it although it was static not dynamic adatation you suggested.

could you please explain more? I'm not sure I understand what
was the configuration (what is static adaptation?).

> However problem was media-stream data so zlib, lzam added just pointless
> overhead.

would that overhead be bigger than a full-blown I/O request to
another block device (potentially slow, or under load, etc. etc.)?

	-ss