linux-kernel - Re: [dm-devel] [PATCH v5] fault-injection: introduce kvmalloc fallback options

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Message-ID: <alpine.LRH.2.02.1804251853460.31135@file01.intranet.prod.int.rdu2.redhat.com>
Date:   Wed, 25 Apr 2018 18:56:49 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@...hat.com>
To:     David Rientjes <rientjes@...gle.com>
cc:     James Bottomley <James.Bottomley@...senpartnership.com>,
        dm-devel@...hat.com, eric.dumazet@...il.com, mst@...hat.com,
        netdev@...r.kernel.org, jasowang@...hat.com,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-kernel@...r.kernel.org, Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org,
        edumazet@...gle.com, Andrew Morton <akpm@...ux-foundation.org>,
        virtualization@...ts.linux-foundation.org,
        David Miller <davem@...emloft.net>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [dm-devel] [PATCH v5] fault-injection: introduce kvmalloc fallback
 options



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