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[209.85.218.52]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5733bebb6bfsm7639687a12.28.2024.05.14.09.04.33 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 14 May 2024 09:04:33 -0700 (PDT) Received: by mail-ej1-f52.google.com with SMTP id a640c23a62f3a-a5a88339780so45770566b.0 for ; Tue, 14 May 2024 09:04:33 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCXcjMdtBzOvpa1nxxK9TP1LqBti5Ho3txnw1N8HPSbOVXHG9h6Rj4LDKxZLicrTbQ/MvlkxYngD+8XzGYDkno81sTs= X-Received: by 2002:a17:906:81cf:b0:a59:a7b7:2b8e with SMTP id a640c23a62f3a-a5a2d5853b3mr843134566b.29.1715702673387; Tue, 14 May 2024 09:04:33 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Linus Torvalds Date: Tue, 14 May 2024 09:04:15 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [LSF/MM/BPF TOPIC] Measuring limits and enhancing buffered IO To: Luis Chamberlain Cc: Al Viro , Kent Overstreet , Matthew Wilcox , lsf-pc@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm , Daniel Gomez , Pankaj Raghav , Jens Axboe , Dave Chinner , Christoph Hellwig , Chris Mason , Johannes Weiner Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 5A74DC0012 X-Rspam-User: X-Stat-Signature: xp3fpyq934hq46j8tobkiqb3cbtzct6q X-HE-Tag: 1715702677-944091 X-HE-Meta: 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 EzK35+oW 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 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: List-Subscribe: List-Unsubscribe: On Tue, 14 May 2024 at 04:52, Luis Chamberlain wrote: > > On Mon, Feb 26, 2024 at 02:46:56PM -0800, Linus Torvalds wrote: > > I really haven't tested this AT ALL. I'm much too scared. But I don't > > actually hate how the code looks nearly as much as I *thought* I'd > > hate it. > > Thanks for this, obviously those interested in this will have to test > this and fix the below issues. I've tested for regressions just against > xfs on 4k reflink profile and detected only two failures, generic/095 > fails with a failure rate of about 1/2 or so: > > * generic/095 > * generic/741 Funky. I do *not* see how those can fail due to the change, but that's the point of testing. Somebody who knows those two tests better, and figures out what the difference is would have to get involved. One different thing that my fast-read case does is that it does *NOT* do the crazy dcache coherency thing that the "full" case does, ie the writably_mapped = mapping_writably_mapped(mapping); ... /* * If users can be writing to this folio using arbitrary * virtual addresses, take care of potential aliasing * before reading the folio on the kernel side. */ if (writably_mapped) flush_dcache_folio(folio); but that shouldn't matter on any sane architecture. Sadly, even arm64 counts as "insane" here, because it does the I$ sync using flush_dcache_folio(). I can't tell what architecture the testing was done on, but I assume it was x86, and I assume the above detail is _not_ the cause. Linus