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Date:   Fri, 18 Dec 2020 10:43:24 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Pavel Tatashin <pasha.tatashin@soleen.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        akpm@linux-foundation.org, vbabka@suse.cz, david@redhat.com,
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        linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v4 05/10] mm/gup: migrate pinned pages out of movable zone
Message-ID: <20201218094324.GT32193@dhcp22.suse.cz>
References: <20201217185243.3288048-1-pasha.tatashin@soleen.com>
 <20201217185243.3288048-6-pasha.tatashin@soleen.com>
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On Thu 17-12-20 13:52:38, Pavel Tatashin wrote:
> +	 * 1. Pinned pages: (long-term) pinning of movable pages is avoided
> +	 *    when pages are pinned and faulted, but it is still possible that
> +	 *    address space already has pages in ZONE_MOVABLE at the time when
> +	 *    pages are pinned (i.e. user has touches that memory before
> +	 *    pinning). In such case we try to migrate them to a different zone,
> +	 *    but if migration fails the pages can still end-up pinned in
> +	 *    ZONE_MOVABLE. In such case, memory offlining might retry a long
> +	 *    time and will only succeed once user application unpins pages.

I still dislike this. Pinning can fail so there shouldn't be any reasons
to break MOVABLE constrain for something that can be handled. If
anything there should be a very good reasoning behind this decision
documented.
-- 
Michal Hocko
SUSE Labs