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Date:   Wed, 14 Dec 2022 10:49:33 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     "Huang, Ying" <ying.huang@intel.com>
Cc:     Dave Hansen <dave.hansen@intel.com>,
        Yang Shi <shy828301@gmail.com>, Wei Xu <weixugc@google.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        LKML <linux-kernel@vger.kernel.org>,
        Feng Tang <feng.tang@intel.com>
Subject: Re: memcg reclaim demotion wrt. isolation
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On Wed 14-12-22 10:57:52, Huang, Ying wrote:
> Michal Hocko <mhocko@suse.com> writes:
[...]
> > This makes sense but I suspect that this wasn't intended also for
> > memcg triggered reclaim. This would mean that a memory pressure in one
> > hierarchy could trigger paging out pages of a different hierarchy if the
> > demotion target is close to full.
> 
> It seems that it's unnecessary to wake up kswapd of demotion target node
> in most cases.  Because we will try to reclaim on the demotion target
> nodes in the loop of do_try_to_free_pages().  It may be better to loop
> the zonelist in the reverse order.  Because the demotion targets are
> usually located at the latter of the zonelist.

Reclaiming from demotion targets first would deal with that as well.
Thanks! Let's establish whether this is something we really need/want
fix first.
-- 
Michal Hocko
SUSE Labs