linux-kernel - Re: [PATCH resend] mm/page_alloc: fix comment is __get_free

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Date:   Sat, 16 Dec 2017 12:52:27 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     JianKang Chen <chenjiankang1@...wei.com>,
        mgorman@...hsingularity.net, hannes@...xchg.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        xieyisheng1@...wei.com, guohanjun@...wei.com,
        wangkefeng.wang@...wei.com
Subject: Re: [PATCH resend] mm/page_alloc: fix comment is __get_free_pages

On Fri 15-12-17 12:57:35, Andrew Morton wrote:
> On Fri, 15 Dec 2017 10:36:18 +0100 Michal Hocko <mhocko@...nel.org> wrote:
> 
> > > > 
> > > > So do we care and I will resend the patch in that case or I just drop
> > > > this from my patch queue?
> > > 
> > > Well..  I still think that silently accepting bad input would be bad
> > > practice.  If we can just delete the assertion and have such a caller
> > > reliably blow up later on then that's good enough.
> > 
> > The point is that if the caller checks for the failed allocation then
> > the result is a memory leak.
> 
> That's if page_address(highmem page) returns NULL.  I'm not sure what
> it returns, really - so many different implementations across so many
> different architectures.

I am not sure I follow. We only do care for HIGHMEM, right? And that one
returns NULL unless the high mem page is not kmaped.

> Oh well, it would have been nice to remove that VM_BUG_ON().  Why not
> just leave the code as it is now?  

BUGing on a bogus usage is not popular anymore. Also checking for
something nobody actually does is a bit pointless. I will not insist
though.

-- 
Michal Hocko
SUSE Labs