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Tue, 22 Aug 2023 10:48:55 -0700 (PDT) MIME-Version: 1.0 References: <20230817-free_pcppages_bulk-v1-0-c14574a9f80c@kernel.org> <20230821103225.qntnsotdzuthxn2y@techsingularity.net> In-Reply-To: <20230821103225.qntnsotdzuthxn2y@techsingularity.net> From: Chris Li Date: Tue, 22 Aug 2023 10:48:42 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH RFC 0/2] mm/page_alloc: free_pcppages_bulk safeguard To: Mel Gorman Cc: Andrew Morton , Kemeng Shi , baolin.wang@linux.alibaba.com, Michal Hocko , david@redhat.com, willy@infradead.org, linux-mm@kvack.org, Namhyung Kim , Greg Thelen , linux-kernel@vger.kernel.org, John Sperbeck , Huang Ying , Alexei Starovoitov Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: B7787140003 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: bka46c8kdp3xxj3w1oeas5m6bmbydne3 X-HE-Tag: 1692726537-215371 X-HE-Meta: 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 lOztxrQp aCBeHL8TkZm0sPSYMtBjRA+el9Wcgkt9gkclyQFs5qyuH/Xy5muF8oJdT6FbXlWXpK1vgG3RkIg56g4MqngKbb6wnalX+BZIrV24Of0XY8DHGiiUL0YtvEZ0NATE/kiGD5bNsq4PMIijga4xRvd+7O/p2hpMXZeww3hK9Qna0SjgsE5876NX1e9Iz0nuyQmfzKBM5OMUa/1D0GygPDb+d6B0Tla09/ZKgERIvgzmcTvcujl4y000jxAlv9cPoji3W1wyDfGMHb5MlXYsp2qVuCHYrl+OFccyScLIHcKRxgURqh6u6gdE/1jfMTAxIPUhJHiKLvMJG1pHxfjCDTOe0hlXdkBpMcqZocgJyUuI84GbQqnHnSme7pO2wJXoTL/TjEKdXiwigY3HdRS60ZnaNMqiPmlpYcO797BOvhG0X/Qad9MhhyGVQzjkQH+/NRf5sqGUAc4ruvwJvjQ1VHoPaVCJc7EOZaavTOnhc X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hi Mel, Adding Alexei to the discussion. On Mon, Aug 21, 2023 at 3:32=E2=80=AFAM Mel Gorman wrote: > > On Thu, Aug 17, 2023 at 11:05:22PM -0700, Chris Li wrote: > > In this patch series I want to safeguard > > the free_pcppage_bulk against change in the > > pcp->count outside of this function. e.g. > > by BPF program inject on the function tracepoint. > > > > I break up the patches into two seperate patches > > for the safeguard and clean up. > > > > Hopefully that is easier to review. > > > > Signed-off-by: Chris Li > > This sounds like a maintenance nightmare if internal state can be arbitra= ry > modified by a BPF program and still expected to work properly in all case= s. > Every review would have to take into account "what if a BPF script modifi= es > state behind our back?" Thanks for the feedback. I agree that it is hard to support if we allow BPF to change any internal stage as a rule. That is why it is a RFC. Would you consider it case by case basis? The kernel panic is bad, the first patch is actually very small. I can also change it to generate warnings if we detect the inconsistent state. How about the second (clean up) patch or Keming's clean up version? I can m= odify it to take out the pcp->count if the verdict is just not supporting BPF changing internal state at all. I do wish to get rid of the pindex_min and pindex_max. Thanks Chris