linux-kernel - Re: [PATCH v3 5/7] zram: support idle/huge page writeback

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 28 Nov 2018 15:35:59 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Joey Pabalinas <joeypabalinas@...il.com>
Subject: Re: [PATCH v3 5/7] zram: support idle/huge page writeback

On Tue, 27 Nov 2018 14:54:27 +0900 Minchan Kim <minchan@...nel.org> wrote:

> This patch supports new feature "zram idle/huge page writeback".
> On zram-swap usecase, zram has usually many idle/huge swap pages.
> It's pointless to keep in memory(ie, zram).
> 
> To solve the problem, this feature introduces idle/huge page
> writeback to backing device so the goal is to save more memory
> space on embedded system.
> 
> Normal sequence to use idle/huge page writeback feature is as follows,
> 
> while (1) {
>         # mark allocated zram slot to idle
>         echo all > /sys/block/zram0/idle
>         # leave system working for several hours
>         # Unless there is no access for some blocks on zram,
> 	# they are still IDLE marked pages.
> 
>         echo "idle" > /sys/block/zram0/writeback
> 	or/and
> 	echo "huge" > /sys/block/zram0/writeback
>         # write the IDLE or/and huge marked slot into backing device
> 	# and free the memory.
> }
> 
> By per discussion:
> https://lore.kernel.org/lkml/20181122065926.GG3441@jagdpanzerIV/T/#u,
> 
> This patch removes direct incommpressibe page writeback feature
> (d2afd25114f4, zram: write incompressible pages to backing device)
> so we could regard it as regression because incompressible pages
> doesn't go to backing storage automatically. Instead, usre should
> do it via "echo huge" > /sys/block/zram/writeback" manually.

I'm not in any position to determine the regression risk here.

Why is that feature being removed, anyway?

> If we hear some regression, we could restore the function.

Why not do that now?