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Date:   Mon, 6 Jan 2020 13:53:52 +0100
From:   Michal Hocko <mhocko@kernel.org>
To:     Luigi Semenzato <semenzato@google.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        rafael@kernel.org, akpm@linux-foundation.org, gpike@google.com
Subject: Re: [PATCH 1/2] Documentation: clarify limitations of hibernation
Message-ID: <20200106125352.GB9198@dhcp22.suse.cz>
References: <20191226220205.128664-1-semenzato@google.com>
 <20191226220205.128664-2-semenzato@google.com>
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On Thu 26-12-19 14:02:04, Luigi Semenzato wrote:
[...]
> +Limitations of Hibernation
> +==========================
> +
> +When entering hibernation, the kernel tries to allocate a chunk of memory large
> +enough to contain a copy of all pages in use, to use it for the system
> +snapshot.  If the allocation fails, the system cannot hibernate and the
> +operation fails with ENOMEM.  This will happen, for instance, when the total
> +amount of anonymous pages (process data) exceeds 1/2 of total RAM.
> +
> +One possible workaround (besides terminating enough processes) is to force
> +excess anonymous pages out to swap before hibernating.  This can be achieved
> +with memcgroups, by lowering memory usage limits with ``echo <new limit> >
> +/dev/cgroup/memory/<group>/memory.mem.usage_in_bytes``.  However, the latter
> +operation is not guaranteed to succeed.

I am not familiar with the hibernation process much. But what prevents
those allocations to reclaim memory and push out the anonymous memory to
the swap on demand during the hibernation's allocations?
-- 
Michal Hocko
SUSE Labs