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[209.85.218.53]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-66105735d75sm1983057a12.14.2026.03.05.09.17.55 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Mar 2026 09:17:56 -0800 (PST) Received: by mail-ej1-f53.google.com with SMTP id a640c23a62f3a-b935b8dcab7so1296590166b.1 for ; Thu, 05 Mar 2026 09:17:55 -0800 (PST) X-Forwarded-Encrypted: i=1; AJvYcCXIc97Xl/RlSthIMH3EXltJKMYqeriWda+9WF3BEu9FqzvHB9o8D8gptS7VMC6sy6xBOEMgfb92jg==@kvack.org X-Received: by 2002:a17:907:da8:b0:b90:e20b:acb9 with SMTP id a640c23a62f3a-b93f0ed492amr449349666b.0.1772731075073; Thu, 05 Mar 2026 09:17:55 -0800 (PST) MIME-Version: 1.0 References: <20260305103941.11f1b27d@gandalf.local.home> In-Reply-To: From: Linus Torvalds Date: Thu, 5 Mar 2026 09:17:37 -0800 X-Gmail-Original-Message-ID: X-Gm-Features: AaiRm50MziCc2ZpZgfQkRzw_b1J2hORS0ItOZxFqZ_sDR2-NwymgJYJk3iB9XEk Message-ID: Subject: Re: [GIT PULL] tracing: Fixes for 7.0 To: "David Hildenbrand (Arm)" Cc: Steven Rostedt , Jason Gunthorpe , Leon Romanovsky , Masami Hiramatsu , Mathieu Desnoyers , Huiwen He , Jerome Marchand , Qing Wang , Shengming Hu , Linux-MM , linux-rdma Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 8AA4E10000E X-Rspamd-Server: rspam07 X-Stat-Signature: tre6yb6h4zuiqnjyzypsmfr1yu7yf9ck X-Rspam-User: X-HE-Tag: 1772731078-799149 X-HE-Meta: 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 KHctQsgQ VabUJZ7VNUDD6jEAd5qo8v3KFu3qYq8o4IpNNLr3ubc57DIKTOZhj8itOlEQq8K3CfSjx5FCCzM3mER18H1Y7PxFuJIRlur/+xb/BVkPb2gwB9hxYJjRT8zLxBXyQxWwLOEq0FbRFk93NTJw5a3YOnXPHik9Qf5IBCt6DB5k3MrZLmvXqB+K6tusOyCH+W7bhfPs6BmyaLcG5nixesoo0OKDjm/uVHmD3tld+yq9EwLq/ifpTWuUXxoSgPt6dqiE3+8a+i2vaiC4X7ZxZBiteOJ0c13krV7Nmn+M/ufdzM8EIe/CuyCfW0MKEngTyuemVtaMP+e9tucElbtam8SC9XuXQy4nsxsDk+dL3Z57CkPXFtuLOjDToXshpOSZFI1YI7LGGf/TjPwpH0UgDb1cKq3pdR7y+vrfAU6KFlMuaLdWQEKebfJpk0Er2K7JT+0hd67poHubDb9vixp8m9cB4z2Z+TZ3Bu4wzR9GQiMKIqeoLub21bzACoxGAPFXlY+NWmT2ckAxhacWealPAy0wgUtDpeJwBZe45Mi/i2igBiMsOpznhAFi7y/x/WNfK9qVDhSBMV0kw/peDZfqCWcenfM4INml6dB9mVfeZOG1v4vpOUw4= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 5 Mar 2026 at 09:00, David Hildenbrand (Arm) wrote: > > QEMU traditionally sets MADV_DONTFORK on guest RAM. One reason is to > speed up fork(), because it doesn't need all the guest RAM in fork'ed > child processes. Yes, I think the MADV_DONTFORK thing makes sense on its own - more so than MADV_DOFORK does. Because it's a very valid thing for user space to do exactly for that "speed up fork()" case. It's similar to how we also export a MADV_WIPEONFORK - for a different use-case, where we don't want the copying behavior (typically because we want the child to re-create its own set of data: I thin the main reason tends to be for things like reseeding random number generation after fork etc). So it's just MADV_DOFORK I don't particularly like, because it had pre-existing kernel semantics (the VM_DONTCOPY bit predates the MADV_* bits by many many years). Not copying on fork is always safe. But copying something that the kernel has said "don't copy" just sounds *wrong*. > > But I get the feeling that maybe we should at least limit MADV_DOFORK > > only to the case where the *source* of the DONTFORK was the user, not > > some kernel mapping. > > ... that makes sense. Forbid toggling it on something that has > VM_SPECIAL set, maybe. Yeah, I think VM_SPECIAL would be a better match than just checking VM_IO. At least it would also catch things like that VM_DONTEXPAND, and PFN mappings. So just changing the existing VM_IO test to cover all the VM_SPECIAL bits would be a simple improvement. Maybe I should just do that and see if anybody even notices (and revert and re-think if somebody does) Linus