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AJvYcCUaAeG1xBB8WkF7xU3nxjs0vYi2aoq6+ZDRK9AqSEv9tYv3KXneZOECA8AcHniwU+twa8352SX47rnDq4Ptb+Biw7KyGoUCIzmbje0= X-Gm-Message-State: AOJu0YyNf1i4PA4LJLdgAwrcbSe8Fhzl+84OhVzKIl4pV0Wb47MudSdf mzv1WjropXdGAm+jp/kUZVoqbDjxBbSkQ2FPfeQ/5tCHa83UwabKHzxoLpUwQCMBKmrjfZkYDrW s X-Google-Smtp-Source: AGHT+IFH1AIy/7QctRVFBr2d16OquKkeqZSHYZCwH83jxFjNpHuXzdUulKBWnEmaOBuftKVbZ+FFFg== X-Received: by 2002:a05:6e02:1a2e:b0:363:cec2:e344 with SMTP id g14-20020a056e021a2e00b00363cec2e344mr2718705ile.2.1710358813639; Wed, 13 Mar 2024 12:40:13 -0700 (PDT) Received: from [192.168.1.116] ([96.43.243.2]) by smtp.gmail.com with ESMTPSA id r11-20020a92c5ab000000b00363c90b1207sm1429ilt.55.2024.03.13.12.40.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 13 Mar 2024 12:40:12 -0700 (PDT) Message-ID: <3429f79b-442c-4444-b592-85090e0e78cd@kernel.dk> Date: Wed, 13 Mar 2024 13:40:11 -0600 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: brd in a memdesc world To: Matthew Wilcox Cc: Christoph Hellwig , linux-block@vger.kernel.org, Pankaj Raghav , Tetsuo Handa References: Content-Language: en-US From: Jens Axboe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/12/24 11:40 AM, Matthew Wilcox wrote: > Hi Jens, > > I'm looking for an architecture-level decision on what the brd driver > should look like once struct page has been shrunk to a minimal size > (more detail at https://kernelnewbies.org/MatthewWilcox/Memdescs ) > > Currently brd uses page->index as a debugging check. In the memdesc > future, struct page has no members (you could store a small amount of > information in it, but I'm not willing to commit to more than a few bits). > > brd doesn't use anything else from struct page, as far as I can tell. > It just calls kmap_atomic() / __free_page() / flush_dcache_page() (and > it doesn't need to call flush_dcache_page() because you can't mmap the > pages in the brd's array). > > Now if you have plans to, eg, support page migration, you're going to need > a bit more infrastructure than just allocating pages, but for what you > have at the moment, just removing the debugging checks that page->index == > idx would make you entirely compatible with the memdesc future. > > Any problem with that? As far as I can recall, I haven't seen that debugging trigger anything in forever. So fine to kill it, imho. -- Jens Axboe