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From:   Luigi Semenzato <semenzato@google.com>
Date:   Mon, 27 Jan 2020 08:13:21 -0800
Message-ID: <CAA25o9QuA_9EoivWo-DuJsWoHCdBm2wio3G8JYxuTfQErT42kg@mail.gmail.com>
Subject: Re: [PATCH 1/2] Documentation: clarify limitations of hibernation
To:     Michal Hocko <mhocko@kernel.org>
Cc:     Linux Memory Management List <linux-mm@kvack.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Geoff Pike <gpike@google.com>
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On Mon, Jan 27, 2020 at 6:16 AM Michal Hocko <mhocko@kernel.org> wrote:
>
> On Fri 24-01-20 08:37:12, Luigi Semenzato wrote:
> [...]
> > The purpose of my documentation patch was to make it clearer that
> > hibernation may fail in situations in which suspend-to-RAM works; for
> > instance, when there is no swap, and anonymous pages are over 50% of
> > total RAM.  I will send a new version of the patch which hopefully
> > makes this clearer.
>
> I was under impression that s2disk is pretty much impossible without any
> swap.

I am not sure what you mean by "swap" here.  S2disk needs a swap
partition for storing the image, but that partition is not used for
regular swap.  If there is no swap, but more than 50% of RAM is free
or reclaimable, s2disk works fine.  If anonymous is more than 50%,
hibernation can still work, but swap needs to be set up (in addition
to the space for the hibernation image).  The setup is not obvious and
I don't think that the documentation is clear on this.

> --
> Michal Hocko
> SUSE Labs