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h=Date:From:To:Cc:Subject:In-Reply-To:References; b=hrEk5wHDENIjlMUpYglMp8AUOxthBoNHko2cDBo4ILhPkeNeGv2vbzVajd5Cl9KfZ r8kXXsvuRJo4k6nCzL+cAmjIX2Fcqm3OH37dKA4zq5jQ7cn9cTcWxFOrJfszmY8k1h cDxyhIGIMzo11FQs4+okpNRoF+TcEYUhcJFsCUWI= Date: Thu, 6 Aug 2026 14:20:02 -0700 From: Andrew Morton To: Johannes Weiner Cc: Jianlin Shi , linux-mm@kvack.org, vbabka@kernel.org, surenb@google.com, mhocko@suse.com, jackmanb@google.com, ziy@nvidia.com, linux-kernel@vger.kernel.org, Joel Granados Subject: Re: [PATCH v5] mm/page_alloc: only update lowmem_reserve_ratio on sysctl write Message-Id: <20260806142002.ac4a349730f3ce15154a71a5@linux-foundation.org> In-Reply-To: References: X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 9559C140010 X-Stat-Signature: wzocggaypstiapaws3tomnt7gtitsksk X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1786051204-244253 X-HE-Meta: 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 rCtVs4lK Xw/7+p9Dgg6hi5PEpWyDCuOsOgSjsr+3WaqNscQSLlAKrlFm9LsTQy1w2J3DmalFc7HfV/p4I13u1Vh+AUMTWfsAZcIRpjb4hACqgZD8UJ5d9t6foIGY7ieT3OXYcM8/e4wkTCUu8U6+0kOGFZe8qPwxB/PysJ9ibNTbNaVgKLgjdhggE2JfZPbhjAtJgnjFbkyMbsfj6BadMH2yHdhLh/tt0rVybLrAtooA0VfaYKvuui9LxM1cypknzGB+iIVnwGF3KKtwgQKeqaZlYG4aAyDoO1mdbsJowfwKrX/1OZPx5VG294hBuUMUXptDhugwgR37N0f/U5w7fXWJUZoALvArIJIJdKwEWYY0GA25G1T7NQ0VbQlXBzjOEBfIFr9MePh5exexAYvIPG+sgr8wBMEX6J3gLe0AkDQgZJcKi6/LjBFaEmFBVYl02XQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 6 Aug 2026 09:50:16 -0400 Johannes Weiner wrote: > > - proc_dointvec_minmax(table, write, buffer, length, ppos); > > + if (!write) > > + return proc_dointvec_minmax(table, write, buffer, length, ppos); > > > > - for (i = 0; i < MAX_NR_ZONES; i++) { > > - if (sysctl_lowmem_reserve_ratio[i] < 1) > > - sysctl_lowmem_reserve_ratio[i] = 0; > > - } > > This could use a comment. How about: > > /* > * proc_dointvec_max() works incrementally. Use a buffer > * and only set the values if all of them parse cleanly. > */ > I added a fixlet: --- a/mm/page_alloc.c~mm-page_alloc-only-update-lowmem_reserve_ratio-on-sysctl-write-fix +++ a/mm/page_alloc.c @@ -6932,6 +6932,10 @@ static int lowmem_reserve_ratio_sysctl_h if (!write) return proc_dointvec_minmax(table, write, buffer, length, ppos); + /* + * proc_dointvec_max() works incrementally. Use a buffer and only set + * the values if all of them parse cleanly. + */ memcpy(ratio, sysctl_lowmem_reserve_ratio, sizeof(ratio)); tmp.data = ratio; _ Sashiko got all upset about concurrency issues: https://sashiko.dev/#/patchset/tencent_A860C873956A52E26AD8D309A308A241BA08@qq.com But I think I'm hearing from Joel is that the longer-term plan is to fix all this up within proc_dointvec_minmax()?