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From:   Jason Gunthorpe <jgg@mellanox.com>
To:     Michal Hocko <mhocko@kernel.org>
CC:     Arnd Bergmann <arnd@arndb.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
        Bernard Metzler <bmt@zurich.ibm.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: add dummy can_do_mlock() helper
Thread-Topic: [PATCH] mm: add dummy can_do_mlock() helper
Thread-Index: AQHVZ08q5wbucvrEOU+F8Ef7pGgfzKckfwoAgAAZK4A=
Date:   Tue, 10 Sep 2019 08:40:37 +0000
Message-ID: <20190910084035.GB2835@mellanox.com>
References: <20190909204201.931830-1-arnd@arndb.de>
 <20190910071030.GG2063@dhcp22.suse.cz>
In-Reply-To: <20190910071030.GG2063@dhcp22.suse.cz>
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On Tue, Sep 10, 2019 at 09:10:30AM +0200, Michal Hocko wrote:
> On Mon 09-09-19 22:41:40, Arnd Bergmann wrote:
> > On kernels without CONFIG_MMU, we get a link error for the siw
> > driver:
> >=20
> > drivers/infiniband/sw/siw/siw_mem.o: In function `siw_umem_get':
> > siw_mem.c:(.text+0x4c8): undefined reference to `can_do_mlock'
> >=20
> > This is probably not the only driver that needs the function
> > and could otherwise build correctly without CONFIG_MMU, so
> > add a dummy variant that always returns false.
> >=20
> > Fixes: 2251334dcac9 ("rdma/siw: application buffer management")
> > Suggested-by: Jason Gunthorpe <jgg@mellanox.com>
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>=20
> Makes sense
> Acked-by: Michal Hocko <mhocko@suse.com>
>=20
> but IB on nonMMU? Whut? Is there any HW that actually supports this?
> Just wondering...

I've never heard of anyone doing this configuration, and I don't
really know much about nommu to comment if it could even potentially
work or not..

Jason