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[24.6.216.183]) by smtp.gmail.com with ESMTPSA id n1-20020a170902e54100b00177ff4019d9sm3356279plf.274.2022.10.30.21.09.38 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Sun, 30 Oct 2022 21:09:39 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3696.120.41.1.1\)) Subject: Re: [PATCH 01/13] mm: Update ptep_get_lockless()s comment From: Nadav Amit In-Reply-To: Date: Sun, 30 Oct 2022 21:09:37 -0700 Cc: Peter Zijlstra , Jann Horn , John Hubbard , X86 ML , Matthew Wilcox , Andrew Morton , kernel list , Linux-MM , Andrea Arcangeli , "Kirill A . Shutemov" , jroedel@suse.de, ubizjak@gmail.com, Alistair Popple Content-Transfer-Encoding: quoted-printable Message-Id: References: <20221022111403.531902164@infradead.org> <20221022114424.515572025@infradead.org> <2c800ed1-d17a-def4-39e1-09281ee78d05@nvidia.com> <6C548A9A-3AF3-4EC1-B1E5-47A7FFBEB761@gmail.com> <47678198-C502-47E1-B7C8-8A12352CDA95@gmail.com> <140B437E-B994-45B7-8DAC-E9B66885BEEF@gmail.com> To: Linus Torvalds X-Mailer: Apple Mail (2.3696.120.41.1.1) ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1667189382; a=rsa-sha256; cv=none; b=RxPPpn0drgHB/VbBqFGn4F78cdZ5c0jWuTM/HpJNAbAnHwQM5yyrvXAGxjEhCq5/hukV+h U4xQ3+Wrw4VWfqciYbbQo7Rc9Q4GYAIDGg+9dDBf/I/AtS4HGf5c9jrxyLR3Fa9WGjjxUQ 7mHf90R9koQdrtE18ulfTXpdFOWmlnI= ARC-Authentication-Results: i=1; imf19.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=kvSxwDiw; spf=pass (imf19.hostedemail.com: domain of nadav.amit@gmail.com designates 209.85.216.43 as permitted sender) smtp.mailfrom=nadav.amit@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1667189382; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=gWemLfOzUXoCZKBHkTng8WZ7m1m/5k1ivUxEwj3raDw=; b=foL6qC8MPD3qSN5nn27nE9+qqdf14bgwBjpYvbWVP7lmNNkwUwlGdPORToSbnYLaee267O TTq6Jjvp4mA5PsZG3jP1G/ASiYgEjfOUCtw+tPJkVZ39yTzgUzYnnNUt88xSgK5k6OWxFC r0OV/uEYPOoCdU3kbzotKXm3HoNpTzs= X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 935801A0007 X-Rspam-User: X-Stat-Signature: ua14mktcowzk8dxxaraisbszstt6h8yq Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=kvSxwDiw; spf=pass (imf19.hostedemail.com: domain of nadav.amit@gmail.com designates 209.85.216.43 as permitted sender) smtp.mailfrom=nadav.amit@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-HE-Tag: 1667189382-928261 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: On Oct 30, 2022, at 6:47 PM, Linus Torvalds = wrote: > The reason I haven't actually tested it is partly because I never > recreated the original problem Navav reported, and partly because the > meat of patch 4/4 is just the same "encode an extra flag bit in the > low bit of the page pointer" that I _did_ test, just doing the "remove > rmap" instead of "set dirty". >=20 > In other words, I *think* this should make Nadav's test-case happy, > and avoid the warning he saw. I am sorry for not managing to make it reproducible on your system. The = fact that you did not get the warning that I got means that it is not a hardware-TLB differences issue (at least not only that), but the race = does not happen on your system (assuming you used ext4 on the BRD). Anyhow, I ran the tests with the patches and there are no failures. Thanks for addressing this issue. I understand from the code that you decided to drop the deferring of set_page_dirty(), which could - at least for the munmap case (where mmap_lock is taken for write) - prevent the need for =E2=80=9Cforce_flush=E2= =80=9D and potentially save TLB flushes. I was just wondering whether the reason for that is that you wanted to have small backportable and conservative patches, or whether you changed your mind about it.