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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1765852992; bh=Jv+loXTV6g1KUJ460fIBTUxe3Rs4OvN9h29r0spZSI8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=FiJ4d/kCgSuS3a8cUgEaXzpdGvtzN295Q1wqZ76AfXUDvQyKnr1ejNcIKaF4wd6db smH0gQiHsAyD4vmEiFcoSBp4c5XuXri2f02uqS2nbw+Yh0azNf/8FkYwwXhCp1lf93 xl0tRxX3OULgVWLItCVQQhV8wY2lwoTAwCTFECwQMh3Dsi6jaC9D0S4ZSeSvrO0NDh YVN9nbfS32jp+Qc2DEP8o9647nhQVLE+yLiF47nvq25+JY9PMlktq9ERwB49ZqTDzk Iz/u5c+w03bVuyUG7CKZVMSckKdYitnSWM4QOvxXqeQsy1KIFcvLlpHcv+NCPkyAXp ufA1BM3VutRtg== Message-ID: Date: Tue, 16 Dec 2025 03:43:03 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH next 0/2] THP COW support for private executable file mmap To: zhangqilong , Matthew Wilcox Cc: "akpm@linux-foundation.org" , "lorenzo.stoakes@oracle.com" , "corbet@lwn.net" , "ziy@nvidia.com" , "baolin.wang@linux.alibaba.com" , "Liam.Howlett@oracle.com" , "npache@redhat.com" , "ryan.roberts@arm.com" , "dev.jain@arm.com" , "baohua@kernel.org" , "lance.yang@linux.dev" , "vbabka@suse.cz" , "rppt@kernel.org" , "surenb@google.com" , "mhocko@suse.com" , "Wangkefeng (OS Kernel Lab)" , Sunnanyong , "linux-mm@kvack.org" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" References: From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: E6FB9140007 X-Stat-Signature: ahbwicfztrbcu8igg8778yzewaphusa3 X-HE-Tag: 1765852993-702946 X-HE-Meta: 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 KISUgyWj DiQQGd8tWMFcp9msBuTj3P7MhHnlmlai9wZD6GohHYUCQzEWHoVDatSsv8C9MFkmOC0nYtwlX0uhZfAP7KseGdQ3rwERriZb2jYjzq2zmY647LDD+pjytovsi7fdVqPbTzkfhWMIBPwM3ojS3Gv8OfZYh/MCCxr1SQPFlkq/Gz61qjtJKEX1iaTR4ylMxhVxCDEAypM7kKAEUOnn1Rhz+4ZKi4wNrPL3/F4OeronxgDx8lPUSKcj0SMwTsXEMZJzn9WUxJxzjsHbNlllFEKHOeQSMrJz/bhTR7/QUKi5lWjB0MDg= 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 12/16/25 03:24, zhangqilong wrote: > > On 12/15/25 15:00, Matthew Wilcox wrote: >>> On Mon, Dec 15, 2025 at 08:34:05PM +0800, Zhang Qilong wrote: >>>> This patch series implementate THP COW for private executable file >>>> mmap. It's major designed to increase the iTLB cache hit rate for hot >>>> patching application, and we add a new sysfs knob to disable or >>>> enable it. >>> >>> You're going to have to provide data to get this patch in. We've >>> deliberately not done this in the past due to memory consumption >> overhead. >>> So you need to prove that's now the wrong decision to make. >>> >>> Microbenchmarks would be a bare minimum, but what are really needed >>> are numbers from actual workloads. >> >> In addition, the sysfs toggle is rather horrible. It's rather clear that this is not a >> system-wide setting to be made, as you likely only want that behavior (if at >> all ...) for a handful of special processes I assume? > > Year, it's not a system-wide setting. We consider enabling this option only when > applying hot patches to special processes. If the sysfs toggle is unavailable, we will > evaluate the overall memory impact on the system after removing it. Thanks very > much for your suggestion. I don't think we want this as any kind of default behavior. But the system toggle is really also not what we want. Could we use some per-VMA or per-file hints to affect the policy? Note that your proposal will likely interact in bad ways with uprobes, after removing uprobes again. -- Cheers David