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[2607:7c80:54:e::133]) by mx.google.com with ESMTPS id k62si18623601pfc.208.2019.02.20.07.02.59 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 20 Feb 2019 07:03:00 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) client-ip=2607:7c80:54:e::133; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=bombadil.20170209 header.b=qZiFOjmG; spf=pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=willy@infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=oZBfBU4jWxNSshmOOtCHrGGSxVl/3qP/1xb30w4GIow=; b=qZiFOjmGGXLVTNULdyIQOXN6j qkQrNwxu5hyCOtMVdQ3zUyEW8qoQaD05FL0B+v8rv8OS5B5Inv+lLU0GITzVKL3d8/w5GQxV2lrdL HIdeMo1PpxLAtqhg+CmHpPmiULTPbmeJXR0/ydG3/rxopoY7aA9SwOP4wElpS1FRulpa26wYdKbLs g2pTzTNz1zwloHDjfcWLkjauRC7zQlFHyVJjibJPIJaKzifpuy95SOmRHPXloeWUTZ1zlP9kOiC7Q hhFYP7riOX85dKjb75YnVopzw7RBdtOtIXyqTZ1k3lxOcOtKDVHXVw71d6Bwbg/vzC6ULoPGhsIBs RCeOIDBBQ==; Received: from willy by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1gwTOf-0005pU-N1; Wed, 20 Feb 2019 15:02:53 +0000 Date: Wed, 20 Feb 2019 07:02:53 -0800 From: Matthew Wilcox To: Will Deacon Cc: Peter Zijlstra , aneesh.kumar@linux.vnet.ibm.com, akpm@linux-foundation.org, npiggin@gmail.com, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux@armlinux.org.uk, heiko.carstens@de.ibm.com, riel@surriel.com, tony.luck@intel.com Subject: Re: [PATCH v6 06/18] asm-generic/tlb: Conditionally provide tlb_migrate_finish() Message-ID: <20190220150253.GH12668@bombadil.infradead.org> References: <20190219103148.192029670@infradead.org> <20190219103233.207580251@infradead.org> <20190219124738.GD8501@fuggles.cambridge.arm.com> <20190219134147.GZ32494@hirez.programming.kicks-ass.net> <20190220144705.GH7523@fuggles.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190220144705.GH7523@fuggles.cambridge.arm.com> User-Agent: Mutt/1.9.2 (2017-12-15) 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 Wed, Feb 20, 2019 at 02:47:05PM +0000, Will Deacon wrote: > On Tue, Feb 19, 2019 at 02:41:47PM +0100, Peter Zijlstra wrote: > > On Tue, Feb 19, 2019 at 12:47:38PM +0000, Will Deacon wrote: > > > Fine for now, but I agree that we should drop the hook altogether. AFAICT, > > > this only exists to help an ia64 optimisation which looks suspicious to > > > me since it uses: > > > > > > mm == current->active_mm && atomic_read(&mm->mm_users) == 1 > > > > > > to identify a "single-threaded fork()" and therefore perform only local TLB > > > invalidation. Even if this was the right thing to do, it's not clear to me > > > that tlb_migrate_finish() is called on the right CPU anyway. > > > > > > So I'd be keen to remove this hook before it spreads, but in the meantime: > > > > Agreed :-) > > > > The obvious slash and kill patch ... untested > > I'm also unable to test this, unfortunately. Can we get it into next after > the merge window and see if anybody reports issues? While I do have a pair of Itanium systems in my basement, neither are sn2 machines, which was the only sub-architecture that implemented tlb_migrate_finish(). I see NASA decomissioned Columbia in 2013, and I imagine most sn2 machines have been similarly scrapped.