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Thu, 16 Mar 2023 15:30:16 +0000 (GMT) X-AuditID: cbfec7f2-ea5ff7000000251f-95-641336088113 Received: from eusmtip1.samsung.com ( [203.254.199.221]) by eusmgms1.samsung.com (EUCPMTA) with SMTP id B1.BD.08862.80633146; Thu, 16 Mar 2023 15:30:16 +0000 (GMT) Received: from CAMSVWEXC02.scsc.local (unknown [106.1.227.72]) by eusmtip1.samsung.com (KnoxPortal) with ESMTPA id 20230316153015eusmtip19802e01efff92dc1fbb3b14a98748063~M7-mBRrTc0360603606eusmtip1h; Thu, 16 Mar 2023 15:30:15 +0000 (GMT) Received: from [192.168.8.107] (106.210.248.172) by CAMSVWEXC02.scsc.local (2002:6a01:e348::6a01:e348) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Thu, 16 Mar 2023 15:29:57 +0000 Message-ID: <367c04f8-f5f6-a628-c4a9-7534fa83eb88@samsung.com> Date: Thu, 16 Mar 2023 16:29:56 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Subject: Re: [LSF/MM/BPF TOPIC] Cloud storage optimizations Content-Language: en-US To: Keith Busch , Luis Chamberlain CC: Matthew Wilcox , Theodore Ts'o , Daniel Gomez , =?UTF-8?Q?Javier_Gonz=c3=a1lez?= , , , , , Dave Chinner , "Christoph Hellwig" From: Pankaj Raghav In-Reply-To: Content-Type: text/plain; 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I'll work on a list of places it currently crashes. > I started looking into this to see why it crashes when we increase the LBA size of a block device greater than the page size. These are my primary findings: - Block device aops (address_space_operations) are all based on buffer head, which limits us to work on only PAGE_SIZE chunks. For a 8k LBA size, the stack trace you posted ultimately fails inside alloc_page_buffers as the size will be > PAGE_SIZE. struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size, bool retry) { struct buffer_head *bh, *head; .... head = NULL; offset = PAGE_SIZE; while ((offset -= size) >= 0) { // we will not go into this loop as offset will be negative ... ... } return head; } - As Dave chinner pointed out later in the thread, we allocate pages in the page cache with order 0, instead of BS of the device or the filesystem. Letting filemap_get_folio(FGP_CREAT) allocate folios in LBA size for a block device should solve that problem, I guess. Is it a crazy idea to convert block device aops (block/fops.c) to use iomap which supports higher order folios instead of mpage and other functions that use buffer head? Let me know your thoughts. -- Pankaj