linux-kernel - Re: [PATCH v7 2/7] mm: introduce external memory hinting API

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Message-ID: <07109fb3-dcf3-0252-4515-7e476fadc259@suse.cz>
Date:   Thu, 12 Mar 2020 13:40:26 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, linux-api@...r.kernel.org,
        oleksandr@...hat.com, Suren Baghdasaryan <surenb@...gle.com>,
        Tim Murray <timmurray@...gle.com>,
        Daniel Colascione <dancol@...gle.com>,
        Sandeep Patil <sspatil@...gle.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Brian Geffon <bgeffon@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        John Dias <joaodias@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Jann Horn <jannh@...gle.com>,
        alexander.h.duyck@...ux.intel.com, sj38.park@...il.com
Subject: Re: [PATCH v7 2/7] mm: introduce external memory hinting API

On 3/10/20 11:20 PM, Minchan Kim wrote:
> On Thu, Mar 05, 2020 at 07:15:10PM +0100, Vlastimil Babka wrote:
>> On 3/2/20 8:36 PM, Minchan Kim wrote:
>> > There is usecase that System Management Software(SMS) want to give
>> > a memory hint like MADV_[COLD|PAGEEOUT] to other processes and
>> > in the case of Android, it is the ActivityManagerService.
>> > 
>> > It's similar in spirit to madvise(MADV_WONTNEED), but the information
>> 
>> You mean MADV_DONTNEED?
> 
> Mean to DONT_NEED's future version.

What's that exactly?

>> 
>> > required to make the reclaim decision is not known to the app.
>> 
>> This seems to be mixing up the differences between MADV_DONTNEED and
>> COLD/PAGEOUT and self-imposed vs external memory hints?
> 
> Sorry, I don't understand what you want here.

You say that process_madvise(MADV_[COLD|PAGEEOUT]) is similar to
madvise(MADV_WONTNEED) but the difference is that the information
required to make the reclaim decision is not known to the app.

I see two differences. One is madvise vs process_madvise, which is explained by
"reclaim decision is not known to the app."
The other is MADV_WONTNEED vs MADV_[COLD|PAGEEOUT], which is... I'm not sure
until you say what's "DONT_NEED's future version" :D

Anyway I assume this part is from the versions where the new COLD and PAGEOUT
flags were introduced together with external memory hinting API?