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Date: Wed, 25 Apr 2018 18:56:49 -0400 (EDT)
From: Mikulas Patocka <mpatocka@redhat.com>
Subject: Re: [dm-devel] [PATCH v5] fault-injection: introduce kvmalloc fallback
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To: David Rientjes <rientjes@google.com>
Cc: James Bottomley <James.Bottomley@hansenpartnership.com>, dm-devel@redhat.com, eric.dumazet@gmail.com, mst@redhat.com, netdev@vger.kernel.org, jasowang@redhat.com, Randy Dunlap <rdunlap@infradead.org>, linux-kernel@vger.kernel.org, Matthew Wilcox <willy@infradead.org>, Michal Hocko <mhocko@kernel.org>, linux-mm@kvack.org, edumazet@google.com, Andrew Morton <akpm@linux-foundation.org>, virtualization@lists.linux-foundation.org, David Miller <davem@davemloft.net>, Vlastimil Babka <vbabka@suse.cz>



On Wed, 25 Apr 2018, David Rientjes wrote:

> On Wed, 25 Apr 2018, Mikulas Patocka wrote:
> 
> > You need to enable it on boot. Enabling it when the kernel starts to 
> > execute userspace code is already too late (because you would miss 
> > kvmalloc calls in the kernel boot path).
> 
> Is your motivation that since kvmalloc() never falls back to vmalloc() on 
> boot because fragmentation is not be an issue at boot that we should catch 
> bugs where it would matter if it had fallen back?  If we are worrying 
> about falling back to vmalloc before even initscripts have run I think we 
> have bigger problems.

The same driver can be compiled directly into the kernel or be loaded as a 
module. If the user (or the person preparing distro kernel) compiles the 
driver directly into the kernel, kvmalloc should be tested on that driver, 
because a different user or distribution can compile that driver as a 
module.

Mikulas