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[209.85.167.45]) by smtp.gmail.com with ESMTPSA id 192sm2004614lfh.28.2019.12.11.17.23.06 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 11 Dec 2019 17:23:06 -0800 (PST) Received: by mail-lf1-f45.google.com with SMTP id b15so353817lfc.4 for ; Wed, 11 Dec 2019 17:23:06 -0800 (PST) X-Received: by 2002:a05:6512:1dd:: with SMTP id f29mr4158153lfp.106.1576113785777; Wed, 11 Dec 2019 17:23:05 -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> In-Reply-To: <1c93194a-ed91-c3aa-deb5-a3394805defb@kernel.dk> From: Linus Torvalds Date: Wed, 11 Dec 2019 17:22:49 -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=0.000000, 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 5:11 PM Jens Axboe wrote: > > 15K is likely too slow to really show an issue, I'm afraid. The 970 > is no slouch, but your crypt setup will likely hamper it a lot. You > don't have a non-encrypted partition on it? No. I normally don't need all that much disk, so I've never upgraded my ssd from the 512G size. Which means that it's actually half full or so, and I never felt like "I should keep an unencrypted partition for IO testing", since I don't generally _do_ any IO testing. I can get my load up with "numjobs=8" and get my iops up to the 100k range, though. But kswapd doesn't much seem to care, the CPU percentage actually does _down_ to 0.39% when I try that. Probably simply because now my CPU's are busy, so they are running at 4.7Ghz instead of the 800Mhz "mostly idle" state ... I guess I should be happy. It does mean that the situation you see isn't exactly the normal case. I understand why you want to do the non-cached case, but the case I think it the worrisome one is the regular buffered one, so that's what I'm testing (not even trying the noaccess patches). So from your report I went "uhhuh, that sounds like a bug". And it appears that it largely isn't - you're seeing it because of pushing the IO subsystem by another order of magnitude (and then I agree that "under those kinds of IO loads, caching just won't help") Linus