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b=wGY3TAx8B0uuobV/pphbkjds+J0vuWBrWQt16W6hkkihQaJbRpkxCvBsWUPClZKLa ChHNE+5h2NRp2Os/J63zgMv4teXIWQI6UOJY00LmASEL7lzCQCPz32asdtGdL1DTKh +U8RqH3PJSK2s+DItB/PyC1R4vFLL+m6ilK321K8= Date: Wed, 26 Feb 2025 15:17:57 -0800 From: Andrew Morton To: Cc: , , , , , , , Subject: Re: [PATCH] mm/page_alloc: make the maximum number of highatomic pageblocks resizable Message-Id: <20250226151757.6e3f4ce355d0fdbc11cd54c0@linux-foundation.org> In-Reply-To: <20250226024126.3718-1-zhongjinji@honor.com> References: <20250226024126.3718-1-zhongjinji@honor.com> X-Mailer: Sylpheed 3.7.0 (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-Rspam-User: X-Stat-Signature: rtjwy67f3td5hamqpy1nqyfb8ipyecp8 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 5411B1C0005 X-HE-Tag: 1740611879-115151 X-HE-Meta: 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 OkOypY7r jz/6MEjzjx9K2pDYMME1pODziKLU0yfBUAHmI3C3q8kIs6XxpHi2WSpBGabAz6eeOjqYq1Ag4rR3Hs17p5940AyXF2lXIpio39ggG99fX/UyimFWh61kluL0hb9FZ7/tbFFZaPedii5PmtOx8+JZ42/U+ESqLvColrocnl6qupSRCXlH0BEolmk5O6oAqWW1tUlfcSvDJaPOSSxuQolA2Oif4hsimNmX5DJfaoR+OZEZaNlffGBCU4eH8R52oxdBsFLySu9+YjCmU7avtg3jSNlVLEXXtU35Nw7ikCwYWyJiLA3Ir5v1G/HqIR3s5cqDgTk4Qv5b3oHMIsrIFqqkZX2jlhVtE5tloZDOR8zuQ0EZLBJJj3GhHF4nGBNXGJrerT8IyHj1xVV+1khG4NBEYqCJSJw== 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 Wed, 26 Feb 2025 10:41:25 +0800 wrote: > From: zhongjinji > > In the past, nr_reserved_highatomic was considered to be part of > unusable_free when there was no ALLOC_RESERVES flag. To prevent > unusable_free from being too large, it is reasonable to set a > fixed maximum highatomic value. Can you explain further? Why is it "reasonable"? Please fully describe the userspace-visible problem which this patch fixes. > Even if the maximum number of highatomic pageblocks is set to be larger, > unusable_free may not increase, since Yu Zhao provided the modification > about nr_free_highatomic in > https://lore.kernel.org/all/20241028182653.3420139-1-yuzhao@google.com/T/#u > > More highatomic pageblocks are beneficial for the successful allocation > of high-order page, which is helpful in some devices. Therefore, use > highatomic_reserve_ratio to adjust the maximum number of highatomic > pageblocks. Can you provide testcases and measurements which help us to understand and to quantify the benefits of this change? > @@ -6199,6 +6201,13 @@ static const struct ctl_table page_alloc_sysctl_table[] = { > .mode = 0644, > .proc_handler = percpu_pagelist_high_fraction_sysctl_handler, > .extra1 = SYSCTL_ZERO, > + }, > + .procname = "highatomic_reserve_ratio", > + .data = &highatomic_reserve_ratio, > + .maxlen = sizeof(highatomic_reserve_ratio), > + .mode = 0644, > + .proc_handler = proc_dointvec_minmax, > + .extra1 = SYSCTL_ZERO, > }, Is there any way at all in which we can address the issue you're seeing without adding yet another tunable? Also, a new highatomic_reserve_ratio should be documented in Documentation/admin-guide/sysctl/vm.rst, please.