linux-kernel - Re: [PATCH v2 0/6] tmpfs: add the option to disable swap

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Date:   Tue, 21 Mar 2023 19:37:45 +0800
From:   haoxin <xhao@...ux.alibaba.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     hughd@...gle.com, akpm@...ux-foundation.org, willy@...radead.org,
        brauner@...nel.org, linux-mm@...ck.org, p.raghav@...sung.com,
        da.gomez@...sung.com, a.manzanares@...sung.com, dave@...olabs.net,
        yosryahmed@...gle.com, keescook@...omium.org,
        patches@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/6] tmpfs: add the option to disable swap


在 2023/3/21 上午5:36, Luis Chamberlain 写道:
> On Mon, Mar 20, 2023 at 07:14:22PM +0800, haoxin wrote:
>> 在 2023/3/20 上午4:32, Luis Chamberlain 写道:
>>> On Tue, Mar 14, 2023 at 10:46:28AM +0800, haoxin wrote:
>>>> All these series looks good to me and i do some test on my virtual machine
>>>> it works well.
>>>>
>>>> so please add Tested-by: Xin Hao<xhao@...ux.alibaba.com>  .
>>>>
>>>> just one question, if tmpfs pagecache occupies a large amount of memory, how
>>>> can we ensure successful memory reclamation in case of memory shortage?
>>> If you're disabling swap then you know the only thing you can do is
>>> unmount if you want to help the VM, otherwise the pressure is just
>>> greater for the VM.
>> Un, what i mean is can we add a priority so that this type of pagecache is
>> reclaimed last ?
> That seems to be a classifier request for something much less aggressive
> than mapping_set_unevictable(). My patches *prior* to using mapping_set_unevictable()
> are I think closer to what it seems you want, but as noted before by
> folks, that also puts unecessary stress on the VM because just fail
> reclaim on our writepage().
>
>> Instead of just setting the parameter noswap to make it unreclaimed, because
>> if such pagecache which occupy big part of memory which can not be
>> reclaimed, it will cause OOM.
> You can't simultaneously retain possession of a cake and eat it, too,
> once you eat it, its gone and noswap eats the cake because of the
> suggestion / decision to follow through with mapping_set_unevictable().
>
> It sounds like you want to make mapping_set_unevictable() optional and
> deal with the possible stress incurred writepage() failing?
Yes, Just a personal idea, in any way, the current patch is an excellent 
implementation,  thank you very much.
>   Not quite
> sure what else to recommend here.
>
>    Luis