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Date:   Thu, 23 Jun 2022 10:05:56 +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@vger.kernel.org,
        cgroups@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] mm: vmpressure: don't count userspace-induced reclaim as
 memory pressure
Message-ID: <YrQe5A+FXnbgOR1f@dhcp22.suse.cz>
References: <20220623000530.1194226-1-yosryahmed@google.com>
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On Thu 23-06-22 00:05:30, Yosry Ahmed wrote:
> Commit e22c6ed90aa9 ("mm: memcontrol: don't count limit-setting reclaim
> as memory pressure") made sure that memory reclaim that is induced by
> userspace (limit-setting, proactive reclaim, ..) is not counted as
> memory pressure for the purposes of psi.
> 
> Instead of counting psi inside try_to_free_mem_cgroup_pages(), callers
> from try_charge() and reclaim_high() wrap the call to
> try_to_free_mem_cgroup_pages() with psi handlers.
> 
> However, vmpressure is still counted in these cases where reclaim is
> directly induced by userspace. This patch makes sure vmpressure is not
> counted in those operations, in the same way as psi. Since vmpressure
> calls need to happen deeper within the reclaim path, the same approach
> could not be followed. Hence, a new "controlled" flag is added to struct
> scan_control to flag a reclaim operation that is controlled by
> userspace. This flag is set by limit-setting and proactive reclaim
> operations, and is used to count vmpressure correctly.
> 
> To prevent future divergence of psi and vmpressure, commit e22c6ed90aa9
> ("mm: memcontrol: don't count limit-setting reclaim as memory pressure")
> is effectively reverted and the same flag is used to control psi as
> well.

Why do we need to add this is a legacy interface now? Are there any
pre-existing users who realized this is bugging them? Please be more
specific about the usecase.

-- 
Michal Hocko
SUSE Labs