linux-kernel - Re: [RFC PATCH V2] zram:calculate available memory when zram is used

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Date:   Sat, 5 Jun 2021 19:07:15 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     yongw.pur@...il.com
Cc:     minchan@...nel.org, ngupta@...are.org, senozhatsky@...omium.org,
        axboe@...nel.dk, akpm@...ux-foundation.org,
        songmuchun@...edance.com, david@...hat.com,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-mm@...ck.org, willy@...radead.org, linux-api@...r.kernel.org
Subject: Re: [RFC PATCH V2] zram:calculate available memory when zram is used

On Sat, Jun 05, 2021 at 09:24:00AM -0700, yongw.pur@...il.com wrote:
> From: wangyong <yongw.pur@...il.com>
> 
> When zram is used, available+Swap free memory is obviously
> bigger than we actually can use, because zram can compress
> memory by compression algorithm and zram compressed data
> will occupy memory too.
> 
> So, we can count the compression ratio of zram in the kernel.
> The space will be saved by zram and other swap device are
> calculated as follows:
> zram[swapfree - swapfree * compress ratio] + swapdev[swapfree]
> We can evaluate the available memory of the whole system as:
> MemAvailable+zram[swapfree - swapfree * compress ratio]+swapdev[swapfree]
> 
> Add an entry to the /proc/meminfo file, returns swap will save space.
> Which name is more appropriate is still under consideration.
> There are several alternative names: SwapAvailable, SwapSaved,
> SwapCompressible
> 
> Signed-off-by: wangyong <yongw.pur@...il.com>
> ---
>  drivers/block/zram/zcomp.h    |  1 +
>  drivers/block/zram/zram_drv.c | 19 +++++++++
>  drivers/block/zram/zram_drv.h |  1 +
>  fs/proc/meminfo.c             |  1 +
>  include/linux/swap.h          | 10 +++++
>  mm/swapfile.c                 | 95 +++++++++++++++++++++++++++++++++++++++++++
>  mm/vmscan.c                   |  1 +
>  7 files changed, 128 insertions(+)

You are adding a new sysfs file with no new Documentation/ABI entry.
Also are you sure you are allowed to add a new proc file entry without
breaking existing tools?

thanks,

greg k-h