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From:   Shakeel Butt <shakeelb@google.com>
Date:   Sat, 16 May 2020 15:35:46 -0700
Message-ID: <CALvZod7euq10j6k9Z_dej4BvGXDjqbND05oM-u6tQrLjosX31A@mail.gmail.com>
Subject: Re: [PATCH] net/packet: simply allocations in alloc_one_pg_vec_page
To:     David Miller <davem@davemloft.net>
Cc:     Eric Dumazet <edumazet@google.com>,
        Willem de Bruijn <willemb@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Sat, May 16, 2020 at 1:40 PM David Miller <davem@davemloft.net> wrote:
>
> From: Shakeel Butt <shakeelb@google.com>
> Date: Fri, 15 May 2020 19:17:36 -0700
>
> > and thus there is no need to have any fallback after vzalloc.
>
> This statement is false.
>
> The virtual mapping allocation or the page table allocations can fail.
>
> A fallback is therefore indeed necessary.

I am assuming that you at least agree that vzalloc should only be
called for non-zero order allocations. So, my argument is if non-zero
order vzalloc has failed (allocations internal to vzalloc, including
virtual mapping allocation and page table allocations, are order 0 and
use GFP_KERNEL i.e. triggering reclaim and oom-killer) then the next
non-zero order page allocation has very low chance of succeeding.