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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:   Wed, 6 Jul 2022 17:14:20 -0700
Message-ID: <CAADnVQLr=ELkgFX2uotfF6KoogqM1DSWdBhvB4J6Pzo9vRypKA@mail.gmail.com>
Subject: Re: [PATCH bpf-next v2 1/2] bpf: Make non-preallocated allocation low priority
To:     Shakeel Butt <shakeelb@google.com>
Cc:     Yafang Shao <laoar.shao@gmail.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai 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 Wed, Jul 6, 2022 at 5:07 PM 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.

hmm. ok. reverted.