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Sat, 22 Jun 2024 14:57:20 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Message-ID: <1a48d05c-539b-4d5d-9375-f2aaa5fa0dd4@I-love.SAKURA.ne.jp> Date: Sat, 22 Jun 2024 14:57:20 +0900 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: mmap_lock: replace get_memcg_path_buf() with on-stack buffer To: Axel Rasmussen , bpf Cc: linux-mm , Andrew Morton , Nicolas Saenz Julienne , LKML References: Content-Language: en-US From: Tetsuo Handa In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 3086520013 X-Stat-Signature: ebib3t48tj8ny5p8kbauj7ik5yor57uw X-Rspam-User: X-HE-Tag: 1719035850-835256 X-HE-Meta: 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 zuhQoOFe JU+IL+iM5oaNYl831zHtbiRe17nPAqErq0s3LPnmbbOM1F8vbChwzYKZ4i6J4tRzB0S/KXZf4sH5rTt3dyychnHuf4Fg8HzBINiLkiXQ0cuW1kgN7Hije/gotIj5e+00q1JklH1TCwCXGsPRjv5DghLHOXI6+7wDKyh7AKmZAlEc+qLvAM7mIiU4DMA+iBze4hSaXurzytNAUMWktxZMz4QJcZkjEVbGn+YSviLrw9jobyrannihdxVkQiervCYY9JsRbDCf86sRB2/hmI9dBCNtlh7A2mUzYlzdQUrYao7yTIufkjpQD8CfIEfXKQWdS1fkeIEVK8bPP01/F+jkVpH/1zJfhRSE/+hYlDHQHRs+1fHV35lY1wmou3A== 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: List-Subscribe: List-Unsubscribe: On 2024/06/22 8:03, Axel Rasmussen wrote: > No objections. Looking back all the way to the first version [1] the > buffers were already percpu, instead of on the stack like this. IOW, > there was no on-list discussion about why this shouldn't go on the > stack. It has been a while, but if memory serves I opted to do it that > way just out of paranoia around putting large buffers on the stack. > But, I agree 256 bytes isn't all that large. > > That v1 patch wasn't all that complex, but then again it didn't deal > with various edge cases properly :) so it has grown significantly more > complex over time. Reconsidering the approach seems reasonable now, > given how much code this removes. > > This change looks straightforwardly correct to me. You can take: > > Reviewed-by: Axel Rasmussen Thank you. One question. CONTEXT_COUNT was defined as below. >> -/* >> - * How many contexts our trace events might be called in: normal, softirq, irq, >> - * and NMI. >> - */ >> -#define CONTEXT_COUNT 4 Is there possibility that this function (or in general, trace events) is called from NMI context? If yes, I worry that functions called from get_mm_memcg_path() are not NMI-safe. Original change at https://lkml.kernel.org/r/3e9b2a54-73d4-48cb-a510-d17984c97a45@I-love.SAKURA.ne.jp was posted due to worrying about NMI safety.