linux-kernel - Re: [PATCH 2/2] zram: idle memory tracking

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Date:   Tue, 27 Mar 2018 10:13:27 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] zram: idle memory tracking

On (03/27/18 10:03), Minchan Kim wrote:
> On Tue, Mar 27, 2018 at 09:49:11AM +0900, Sergey Senozhatsky wrote:
> > On (03/26/18 15:49), Minchan Kim wrote:
> > > zRam as swap is useful for small memory device. However, swap means
> > > those pages on zram are mostly cold pages due to VM's LRU algorithm.
> > > Especially, once init data for application are touched for launching,
> > > they tend to be not accessed any more and finally swapped out.
> > > zRAM can store such cold pages as compressed form but it's pointless
> > > to keep in memory. Better idea is app developers free them directly
> > > rather than remaining them on heap.
> > > 
> > > This patch tell us last accesss time of each block of zram via
> > > "cat /sys/kernel/debug/zram/zram0/access_time".
> > > 
> > > The output is as follows,
> > > 
> > > 276 1250
> > > 277 1800
> > > ..  ..
> > > ..  ..
> > 
> > So can we just use CONFIG_IDLE_PAGE_TRACKING + CONFIG_PAGE_OWNER?
> 
> The goal is not mapped memory tracking but one swapped out.
> Can we do it by above two combination?

Ah, you are right. page_idle tracks only pages which are on LRU lists.

> Furthermore, I am planning to provide incompressible pages as well
> as access time so I will change interface at v2.

OK.

	-ss