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From: yong w <yongw.pur@gmail.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: minchan@kernel.org, ngupta@vflare.org, senozhatsky@chromium.org,
	axboe@kernel.dk, akpm@linux-foundation.org,
	songmuchun@bytedance.com, David Hildenbrand <david@redhat.com>,
	linux-kernel@vger.kernel.org, linux-block@vger.kernel.org,
	linux-mm@kvack.org, willy@infradead.org,
	linux-api@vger.kernel.org, lu.zhongjun@zte.com.cn,
	yang.yang29@zte.com.cn, zhang.wenya1@zte.com.cn,
	wang.yong12@zte.com.cn
Subject: Re: [RFC PATCH V3] zram:calculate available memory when zram is used
Date: Wed, 9 Jun 2021 22:23:36 +0800	[thread overview]
Message-ID: <CAOH5QeBV5zq=SpMSxZHJqgmfKegdgc7ehpots6AKjjgEYq5rGg@mail.gmail.com> (raw)
In-Reply-To: <YL84boGKozWE+n23@kroah.com>

Greg KH <gregkh@linuxfoundation.org> 于2021年6月8日周二 下午5:29写道：

>
> On Mon, Jun 07, 2021 at 08:39:14AM -0700, yongw.pur@gmail.com wrote:
> > From: wangyong <wang.yong12@zte.com.cn>
> >
> > 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]
>
> Why is this needed to be exported by userspace?  Who is going to use
> this information and why can't they just calculate it from the exported
> information already?

In embedded devices, it is necessary to assess how much memory is available.
If the memory allocation is based on available+swapfree, it may cause oom and
affect the normal use of the devices. And it is more accurate and safe
to calculate
the swap available memory through minimum compression ratio.

Although mm_stat interface provides compressed information，but it is not easy to
get the minimum compression ratio during swaping out. Kernel provides a common
interface, which makes it easier to use and judge the state of system memory

> What tool requires this new information and what is it going to be used
> for?

It can be used in embedded devices to evaluate the memory condition
and avoid causing oom; Also If we wants to know more accurate available
memory information when zram is used.

> And why add a block driver's information to a core proc file?  Shouldn't
> the information only be in the block driver's sysfs directory only?
>
> thanks,
>
> greg k-h

I thought it would be better to put it there.
In the first patch, MemAvailable returned with swap available memory, and
David recommended a separate interface.

thanks

  reply	other threads:[~2021-06-09 14:24 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-07 15:39 [RFC PATCH V3] zram:calculate available memory when zram is used yongw.pur
2021-06-08  9:28 ` Greg KH
2021-06-09 14:58   ` yong w
2021-06-08  9:29 ` Greg KH
2021-06-09 14:23   ` yong w [this message]
2021-06-09 14:59     ` Greg KH

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