linux-kernel - Re: [PATCH v7 1/2] mm: introduce process

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Message-ID: <YQzZqFwDP7eUxwcn@dhcp22.suse.cz>
Date:   Fri, 6 Aug 2021 08:41:44 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     Shakeel Butt <shakeelb@...gle.com>,
        David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <guro@...com>, Rik van Riel <riel@...riel.com>,
        Minchan Kim <minchan@...nel.org>,
        Christian Brauner <christian@...uner.io>,
        Christoph Hellwig <hch@...radead.org>,
        Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Florian Weimer <fweimer@...hat.com>,
        Jan Engelhardt <jengelh@...i.de>,
        Tim Murray <timmurray@...gle.com>,
        Linux API <linux-api@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-team <kernel-team@...roid.com>
Subject: Re: [PATCH v7 1/2] mm: introduce process_mrelease system call

On Thu 05-08-21 11:37:06, Suren Baghdasaryan wrote:
[...]
> > One question I have is why mmget() and not mmgrab()? I see mmgrab() in
> > oom_kill.c.
> 
> You are likely right here. The caller's context probably can't be
> considered a "real user" when reaping the mm. However, we take an
> mmap_lock shortly after, so not sure if in practice there is much
> difference.
> Michal, WDYT?

As explained in other response. mmget is to pin address space to not go
away. You do not need that for this purpose. All you need is to pin mm
to not go away. Address space can be unmapped concurrently.
-- 
Michal Hocko
SUSE Labs