linux-kernel - Re: [PATCH 1/2] Documentation: clarify limitations of hibernation

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Date:   Mon, 6 Jan 2020 13:53:52 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Luigi Semenzato <semenzato@...gle.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        rafael@...nel.org, akpm@...ux-foundation.org, gpike@...gle.com
Subject: Re: [PATCH 1/2] Documentation: clarify limitations of hibernation

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