linux-kernel - Re: [PATCH v16.1 0/9] mm / virtio: Provide support for free page reporting

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Message-ID: <286cae85-5dc0-50a7-4fb1-96e75cef408d@amazon.com>
Date:   Fri, 24 Jan 2020 17:40:51 +0100
From:   Alexander Graf <graf@...zon.com>
To:     Hillf Danton <hdanton@...a.com>
CC:     Alexander Duyck <alexander.duyck@...il.com>, <kvm@...r.kernel.org>,
        <mst@...hat.com>, <linux-kernel@...r.kernel.org>,
        <linux-mm@...ck.org>, <akpm@...ux-foundation.org>,
        <mgorman@...hsingularity.net>, Minchan Kim <minchan@...nel.org>,
        <vbabka@...e.cz>
Subject: Re: [PATCH v16.1 0/9] mm / virtio: Provide support for free page
 reporting



On 24.01.20 14:23, Hillf Danton wrote:
> 
> On Thu, 23 Jan 2020 11:20:07 +0100 Alexander Graf wrote:
>>
>> The big problem I see is that what I really want from a user's point of
>> view is a tuneable that says "Automatically free clean page cache pages
>> that were not accessed in the last X minutes".
> 
> A diff is made on top of 1a4e58cce84e ("mm: introduce MADV_PAGEOUT") without
> test in any form, assuming it goes in line with the tunable above but without
> "X minutes" taken into account.
> 
> [BTW, please take a look at
> Content-Type: text/plain; charset="utf-8"; format="flowed"
> Content-Transfer-Encoding: base64
Thanks, looks like Exchange doesn't pass 8bit data on, I've changed the 
default to ascii now, please just notify me in private if you see it 
broken again.

> 
> and ensure pure text message.]
> 
> 
> --- a/include/uapi/asm-generic/mman-common.h
> +++ b/include/uapi/asm-generic/mman-common.h
> @@ -69,6 +69,7 @@
>   
>   #define MADV_COLD	20		/* deactivate these pages */
>   #define MADV_PAGEOUT	21		/* reclaim these pages */
> +#define MADV_CCPC	22		/* reclaim cold & clean page cache pages */

This patch adds a new madvise flag. I have a hard time seeing how that 
would help with the "full system expiry" of pages?

The basic point that I tried to make above was that I would ideally like 
to have a coldness cutoff date at which you can be pretty confident that 
page cache data is no longer needed.

To work properly, this needs to be transparent to any normal process on 
the system :).


Alex



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