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[209.85.167.54]) by smtp.gmail.com with ESMTPSA id o20sm3755285ljc.35.2019.12.12.14.18.22 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 12 Dec 2019 14:18:22 -0800 (PST) Received: by mail-lf1-f54.google.com with SMTP id l18so468916lfc.1 for ; Thu, 12 Dec 2019 14:18:22 -0800 (PST) X-Received: by 2002:ac2:50cc:: with SMTP id h12mr6996151lfm.29.1576189102141; Thu, 12 Dec 2019 14:18:22 -0800 (PST) MIME-Version: 1.0 References: <20191211152943.2933-1-axboe@kernel.dk> <63049728.ylUViGSH3C@merkaba> <7bf74660-874e-6fd7-7a41-f908ccab694e@kernel.dk> In-Reply-To: <7bf74660-874e-6fd7-7a41-f908ccab694e@kernel.dk> From: Linus Torvalds Date: Thu, 12 Dec 2019 14:18:06 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCHSET v3 0/5] Support for RWF_UNCACHED To: Jens Axboe Cc: Martin Steigerwald , Linux-MM , linux-fsdevel , linux-block , Matthew Wilcox , Chris Mason , Dave Chinner Content-Type: text/plain; charset="UTF-8" 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 Thu, Dec 12, 2019 at 7:16 AM Jens Axboe wrote: > > I don't know the nocache tool, but I'm guessing it just does the writes > (or reads) and then uses FADV_DONTNEED to drop behind those pages? > That's fine for slower use cases, it won't work very well for fast IO. > The write side currently works pretty much like that internally, whereas > the read side doesn't use the page cache at all. Well, I think that if we have this RWF/IOC_UNCACHED flag, maybe we should make FADV_NOREUSE file descriptors just use it even for regular read/write.. Right now FADV_NOREUSE is a no-op for the kernel, I think, because we historically didn't have the facility. But FADV_DONTNEED is different. That's for dropping pages after use (ie invalidate_mapping_pages()) Linus