linux-kernel - Re: [PATCH v2 0/5] Introduce MADV_COLD and MADV

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Date:   Wed, 12 Jun 2019 13:37:15 +0200
From:   Pavel Machek <pavel@....cz>
To:     Oleksandr Natalenko <oleksandr@...hat.com>
Cc:     Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-api@...r.kernel.org,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Tim Murray <timmurray@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Daniel Colascione <dancol@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Brian Geffon <bgeffon@...gle.com>, jannh@...gle.com,
        oleg@...hat.com, christian@...uner.io, hdanton@...a.com,
        lizeb@...gle.com
Subject: Re: [PATCH v2 0/5] Introduce MADV_COLD and MADV_PAGEOUT

Hi!

> > > This approach is similar in spirit to madvise(MADV_WONTNEED), but the
> > > information required to make the reclaim decision is not known to the app.
> > > Instead, it is known to a centralized userspace daemon, 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 -
> > > 
> > >     struct pr_madvise_param {
> > >             int size;               /* the size of this structure */
> > >             int cookie;             /* reserved to support atomicity */
> > >             int nr_elem;            /* count of below arrary fields */
> > >             int __user *hints;      /* hints for each range */
> > >             /* to store result of each operation */
> > >             const struct iovec __user *results;
> > >             /* input address ranges */
> > >             const struct iovec __user *ranges;
> > >     };
> > >     
> > >     int process_madvise(int pidfd, struct pr_madvise_param *u_param,
> > >                             unsigned long flags);
> > 
> > That's quite a complex interface.
> > 
> > Could we simply have feel_free_to_swap_out(int pid) syscall? :-).
> 
> I wonder for how long we'll go on with adding new syscalls each time we need
> some amendment to existing interfaces. Yes, clone6(), I'm looking at
> you :(.
> 
> In case of process_madvise() keep in mind it will be focused not only on
> MADV_COLD, but also, potentially, on other MADV_ flags as well. I can
> hardly imagine we'll add one syscall per each flag.

Use case described above talked about whole-process-at-a-time usage,
so I'm asking if simpler interface/code is enough. If there's
motivation for more complex version, it should be described here...

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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