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[209.85.208.179]) by smtp.gmail.com with ESMTPSA id z13sm2056033ljh.21.2019.12.11.17.50.13 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 11 Dec 2019 17:50:13 -0800 (PST) Received: by mail-lj1-f179.google.com with SMTP id e10so361979ljj.6 for ; Wed, 11 Dec 2019 17:50:13 -0800 (PST) X-Received: by 2002:a2e:9ad8:: with SMTP id p24mr4244948ljj.148.1576115413333; Wed, 11 Dec 2019 17:50:13 -0800 (PST) MIME-Version: 1.0 References: <20191211152943.2933-1-axboe@kernel.dk> <0d4e3954-c467-30a7-5a8e-7c4180275533@kernel.dk> <1c93194a-ed91-c3aa-deb5-a3394805defb@kernel.dk> <6e2ca035-0e06-1def-5ea9-90a7466b2d49@kernel.dk> In-Reply-To: <6e2ca035-0e06-1def-5ea9-90a7466b2d49@kernel.dk> From: Linus Torvalds Date: Wed, 11 Dec 2019 17:49:57 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCHSET v3 0/5] Support for RWF_UNCACHED To: Jens Axboe Cc: Linux-MM , linux-fsdevel , linux-block , Matthew Wilcox , Chris Mason , Dave Chinner , Johannes Weiner Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000002, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Dec 11, 2019 at 5:41 PM Jens Axboe wrote: > > So now I'm even more puzzled why your (desktop?) doesn't show it, it > must be more potent than my x1 laptop. But for me, the laptop and 2 > socket test box show EXACTLY the same behavior, laptop is just too slow > to make it really pathological. I see the exact same thing. And now, go do "perf record -a sleep 100" while this is going on, to see the big picture. Suddenly that number is a lot smaller. Because the kswapd cost is less than 10% of one cpu, and the xas_create is 30% of that. IOW, it's not all that dominant until you zoom in on it. Considering the amount of IO going on, it's kind of understandable. But as mentioned, it does look like something that should be fixed. Maybe it's even something where it's a bad XArray case? Willy? Linus