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[24.6.216.183]) by smtp.gmail.com with ESMTPSA id q18-20020a63f952000000b00434760ee36asm1378342pgk.16.2022.10.29.13.56.32 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Sat, 29 Oct 2022 13:56:33 -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: Sat, 29 Oct 2022 13:56:31 -0700 Cc: John Hubbard , Peter Zijlstra , Jann Horn , 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> <2c800ed1-d17a-def4-39e1-09281ee78d05@nvidia.com> <6C548A9A-3AF3-4EC1-B1E5-47A7FFBEB761@gmail.com> <47678198-C502-47E1-B7C8-8A12352CDA95@gmail.com> <3a57cfc5-5db4-bdc9-1ddf-5305a37ffa62@nvidia.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=1667076995; a=rsa-sha256; cv=none; b=e6eQ6UZii13KcUMwhUUXfmjnOa8KjLIRL39w1vCFG3oXm+Bv7rUxhv4HTkXpgMoVPQCZcx 5O08eRv4uJKAj5uCFPGPl9cKE9v7/APtn0pELDe7Oix/jpBA4WHmLFXx3zabmtNGqqrykH P8iZxvekd5UBpFSBzieVQzqPNNCP/rw= ARC-Authentication-Results: i=1; imf16.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b="a0r/sqmp"; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf16.hostedemail.com: domain of nadav.amit@gmail.com designates 209.85.216.45 as permitted sender) smtp.mailfrom=nadav.amit@gmail.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1667076995; 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=a7WlHZh5vviFw19hFMjNhkQcVi4vYscxdo+Dmp4kQDE=; b=zpZscw3T1rymOcY2iuhVBojyyFYTWYzWiitku36tCmPxxbp1uog04om1Uyo14YD81LbHnd mNcd+khAFOdTQx9ec7s8DL0eDSMIQ/2yZvI1S33j0AAM8I9kn6E90YReCCNtNPclIaYYHt kAqZa+663oDng/sx5TAZO6TDziZF9YE= X-Rspam-User: Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b="a0r/sqmp"; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf16.hostedemail.com: domain of nadav.amit@gmail.com designates 209.85.216.45 as permitted sender) smtp.mailfrom=nadav.amit@gmail.com X-Stat-Signature: 5f6nnpahnygdfrwrfrct18z9zm4re75s X-Rspamd-Queue-Id: 8B07A180004 X-Rspamd-Server: rspam06 X-HE-Tag: 1667076995-747392 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 29, 2022, at 1:15 PM, Linus Torvalds = wrote: > (b) we could move the "page_remove_rmap()" into the "flush-and-free" = path too >=20 > And (b) would be fairly easy - same model as that dirty bit patch, > just a 'do page_remove_rmap too' - except page_remove_rmap() wants the > vma as well (and we delay the TLB flush over multiple vma's, so it's > not just a "save vma in mmu_gather=E2=80=9D). (b) sounds reasonable and may potentially allow future performance improvements (batching, doing stuff without locks). It does appear to break a potential hidden assumption that rmap is = removed while the ptl is acquired (at least in the several instances I samples). Yet, anyhow page_vma_mapped_walk() checks the PTE before calling the function, so it should be fine. I=E2=80=99ll give it a try.