linux-kernel - Re: [PATCH] mm: add dummy can_do

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Date:   Tue, 10 Sep 2019 08:40:37 +0000
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        Bernard Metzler <bmt@...ich.ibm.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: add dummy can_do_mlock() helper

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:
> > 
> > drivers/infiniband/sw/siw/siw_mem.o: In function `siw_umem_get':
> > siw_mem.c:(.text+0x4c8): undefined reference to `can_do_mlock'
> > 
> > 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.
> > 
> > Fixes: 2251334dcac9 ("rdma/siw: application buffer management")
> > Suggested-by: Jason Gunthorpe <jgg@...lanox.com>
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> 
> Makes sense
> Acked-by: Michal Hocko <mhocko@...e.com>
> 
> 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