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References: <20220706155848.4939-1-laoar.shao@gmail.com> <20220706155848.4939-2-laoar.shao@gmail.com>
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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Thu, 7 Jul 2022 08:44:37 -0700
Message-ID: <CAADnVQKJ44nmxzUDAkckXJ2mzJAshvzzGFP-oPT=NO3rGW7pQA@mail.gmail.com>
Subject: Re: [PATCH bpf-next v2 1/2] bpf: Make non-preallocated allocation low priority
To:     Yafang Shao <laoar.shao@gmail.com>
Cc:     Shakeel Butt <shakeelb@google.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>, Martin Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        john fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Quentin Monnet <quentin@isovalent.com>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Hao Luo <haoluo@google.com>, bpf <bpf@vger.kernel.org>,
        Linux MM <linux-mm@kvack.org>
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On Thu, Jul 7, 2022 at 3:28 AM Yafang Shao <laoar.shao@gmail.com> wrote:
>
> On Thu, Jul 7, 2022 at 8:07 AM Shakeel Butt <shakeelb@google.com> wrote:
> >
> > On Wed, Jul 06, 2022 at 03:58:47PM +0000, Yafang Shao wrote:
> > > GFP_ATOMIC doesn't cooperate well with memcg pressure so far, especially
> > > if we allocate too much GFP_ATOMIC memory. For example, when we set the
> > > memcg limit to limit a non-preallocated bpf memory, the GFP_ATOMIC can
> > > easily break the memcg limit by force charge. So it is very dangerous to
> > > use GFP_ATOMIC in non-preallocated case. One way to make it safe is to
> > > remove __GFP_HIGH from GFP_ATOMIC, IOW, use (__GFP_ATOMIC |
> > > __GFP_KSWAPD_RECLAIM) instead, then it will be limited if we allocate
> > > too much memory.
> >
> > Please use GFP_NOWAIT instead of (__GFP_ATOMIC | __GFP_KSWAPD_RECLAIM).
> > There is already a plan to completely remove __GFP_ATOMIC and mm-tree
> > already have a patch for that.
> >
>
> After reading the discussion[1], it looks good to me to use GFP_NOWAIT
> instead. I will update it.

Should we use GFP_ATOMIC | __GFP_NOMEMALLOC instead
to align with its usage in the networking stack?