netdev - Re: [PATCH] net/packet: simply allocations in alloc_one_pg_vec

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Message-ID: <CANn89iJ9BYNi__DhLp_QE5JU7=RxkzknOSxD+P+qiHg2=Ho6Ow@mail.gmail.com>
Date:   Sat, 16 May 2020 15:45:46 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     David Miller <davem@...emloft.net>,
        Willem de Bruijn <willemb@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net/packet: simply allocations in alloc_one_pg_vec_page

On Sat, May 16, 2020 at 3:35 PM Shakeel Butt <shakeelb@...gle.com> wrote:
>
> On Sat, May 16, 2020 at 1:40 PM David Miller <davem@...emloft.net> wrote:
> >
> > From: Shakeel Butt <shakeelb@...gle.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.


32bit kernels might have exhausted their vmalloc space, yet they can
still allocate order-0 pages.