linux-kernel - Re: [PATCH v2] mm: Add MREMAP

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Message-ID: <87eevh3zms.fsf@oldenburg2.str.redhat.com>
Date:   Thu, 30 Jan 2020 13:19:39 +0100
From:   Florian Weimer <fweimer@...hat.com>
To:     Brian Geffon <bgeffon@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, linux-api@...r.kernel.org,
        Andy Lutomirski <luto@...capital.net>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Yu Zhao <yuzhao@...gle.com>, Jesse Barnes <jsbarnes@...gle.com>
Subject: Re: [PATCH v2] mm: Add MREMAP_DONTUNMAP to mremap().

* Brian Geffon:

> Hi Florian,
> copy_vma will make a copy of the existing VMA leaving the old VMA
> unchanged, so the source keeps its existing protections, this is what
> makes it very useful along with userfaultfd.

I see.  On the other hand, it's impossible to get the PROT_NONE behavior
by a subsequent mprotect call because the mremap has to fail in some
cases in vm.overcommit_memory=2 mode.  But maybe that other behavior can
be provided with a different flag if it turns out to be useful in the
future.

Thanks,
Florian