Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 23 Jun 2022 18:37:02 +0200
From:   Michal Hocko <mhocko@suse.com>
To:     Yosry Ahmed <yosryahmed@google.com>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Shakeel Butt <shakeelb@google.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Matthew Wilcox <willy@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        David Hildenbrand <david@redhat.com>,
        Miaohe Lin <linmiaohe@huawei.com>, NeilBrown <neilb@suse.de>,
        Alistair Popple <apopple@nvidia.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Peter Xu <peterx@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Cgroups <cgroups@vger.kernel.org>, Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH] mm: vmpressure: don't count userspace-induced reclaim as
 memory pressure
Message-ID: <YrSWruhPlJV1X9kp@dhcp22.suse.cz>
References: <20220623000530.1194226-1-yosryahmed@google.com>
 <YrQe5A+FXnbgOR1f@dhcp22.suse.cz>
 <CAJD7tkanavKpKrQr8-jA8pukgD7OY4eOwJRZufJ2NoThD12G+Q@mail.gmail.com>
 <YrQ1o3CeaZWhm+h4@dhcp22.suse.cz>
 <CAJD7tkadsLOV7GMFAm+naX4Y1WpZ-4=NkAhAMxNw60iaRPWx=w@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAJD7tkadsLOV7GMFAm+naX4Y1WpZ-4=NkAhAMxNw60iaRPWx=w@mail.gmail.com>
Precedence: bulk

On Thu 23-06-22 09:22:35, Yosry Ahmed wrote:
> On Thu, Jun 23, 2022 at 2:43 AM Michal Hocko <mhocko@suse.com> wrote:
> >
> > On Thu 23-06-22 01:35:59, Yosry Ahmed wrote:
[...]
> > > In our internal version of memory.reclaim that we recently upstreamed,
> > > we do not account vmpressure during proactive reclaim (similar to how
> > > psi is handled upstream). We want to make sure this behavior also
> > > exists in the upstream version so that consolidating them does not
> > > break our users who rely on vmpressure and will start seeing increased
> > > pressure due to proactive reclaim.
> >
> > These are good reasons to have this patch in your tree. But why is this
> > patch benefitial for the upstream kernel? It clearly adds some code and
> > some special casing which will add a maintenance overhead.
> 
> It is not just Google, any existing vmpressure users will start seeing
> false pressure notifications with memory.reclaim. The main goal of the
> patch is to make sure memory.reclaim does not break pre-existing users
> of vmpressure, and doing it in a way that is consistent with psi makes
> sense.

memory.reclaim is v2 only feature which doesn't have vmpressure
interface. So I do not see how pre-existing users of the upstream kernel
can see any breakage.

-- 
Michal Hocko
SUSE Labs