linux-kernel - Re: [PATCH v8 0/4] introduce memory hinting API for external process

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Date:   Tue, 23 Jun 2020 10:59:44 +0200
From:   Oleksandr Natalenko <oleksandr@...hat.com>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        linux-mm <linux-mm@...ck.org>, linux-api@...r.kernel.org,
        Suren Baghdasaryan <surenb@...gle.com>,
        Tim Murray <timmurray@...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,
        David Rientjes <rientjes@...gle.com>,
        Arjun Roy <arjunroy@...gle.com>
Subject: Re: [PATCH v8 0/4]  introduce memory hinting API for external process

Hello.

On Mon, Jun 22, 2020 at 12:36:35PM -0700, Minchan Kim wrote:
> On Mon, Jun 22, 2020 at 12:28:56PM -0700, Minchan Kim wrote:
> > Now, we have MADV_PAGEOUT and MADV_COLD as madvise hinting API. With that,
> > application could give hints to kernel what memory range are preferred to be
> > reclaimed. However, in some platform(e.g., Android), the information
> > required to make the hinting decision is not known to the app.
> > Instead, it is known to a centralized userspace daemon(e.g., ActivityManagerService),
> > and that daemon must be able to initiate reclaim on its own without any app
> > involvement.
> > 
> > To solve the concern, this patch introduces new syscall - process_madvise(2).
> > Bascially, it's same with madvise(2) syscall but it has some differences.
> > 
> > 1. It needs pidfd of target process to provide the hint
> > 2. It supports only MADV_{COLD|PAGEOUT} at this moment.
> >    Other hints in madvise will be opened when there are explicit requests from
> >    community to prevent unexpected bugs we couldn't support.
> > 3. Only privileged processes can do something for other process's address
> >    space.
> > 
> > For more detail of the new API, please see "mm: introduce external memory hinting API"
> > description in this patchset.
> > 
> > * from v7 -  http://lore.kernel.org/r/20200302193630.68771-1-minchan@kernel.org
> >   * dropping pid support from new syscall and fold releated patches into syscall patch
> >   * dropping KSM patch by discussion - Oleksandr, I lost the discussion.
> >     Please resend the single patch against of the patchset if you resolves the discussion.
> >     https://lore.kernel.org/linux-api/20200302193630.68771-8-minchan@kernel.org/
> 
> Oleksandr, it seems you discussed something with Vlastimil but couldn't
> find conclustion yet and Since Jann put an a new note in the thread,
> I detach the patch from this patchset.
> 
> Please send the KSM patch based on this patchset if you belive there is
> no need to be actionable for comments.

I don't think we came to some definite conclusion, but I'll try to implement
Vlastimil's suggestion and then send it separately for evaluation.

Lets keep KSM bit out of your submission so I won't slow it down.

-- 
  Best regards,
    Oleksandr Natalenko (post-factum)
    Principal Software Maintenance Engineer