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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1tMK2z-00000000MX5-1YvQ; Sat, 14 Dec 2024 04:46:33 +0000 Date: Sat, 14 Dec 2024 04:46:33 +0000 From: Matthew Wilcox To: Luis Chamberlain Cc: hch@lst.de, hare@suse.de, dave@stgolabs.net, david@fromorbit.com, djwong@kernel.org, john.g.garry@oracle.com, ritesh.list@gmail.com, kbusch@kernel.org, linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org, gost.dev@samsung.com, p.raghav@samsung.com, da.gomez@samsung.com, kernel@pankajraghav.com Subject: Re: [RFC v2 05/11] fs/mpage: use blocks_per_folio instead of blocks_per_page Message-ID: References: <20241214031050.1337920-1-mcgrof@kernel.org> <20241214031050.1337920-6-mcgrof@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241214031050.1337920-6-mcgrof@kernel.org> X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 8549720013 X-Stat-Signature: keaibwky15t3s96bks6j6bnakqbb44we X-Rspam-User: X-HE-Tag: 1734151576-914955 X-HE-Meta: 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 dH+Immd5 ZodgCuZKFx9AQVIk9w15VEj1TTheh9h+F0OZz2S+KCdFekpV9DwYU8p2DQEwQVp2TrLZhCefhM+hFcv6F6cxoidWZbWMhbf/OKeLsRknX1lLSUQ3UreZ/gVbhNUPw382h9Yfa3mcoaktqYd05jI/vYU6XVpdcF2x4xr7Izl0C1dI08QPy3aXpqHnAcEzlqmf2MonksUv55C3qUO9VATw7aUDhdyyT0qGPLYy4tDZcpC+ZsVQU59OEKrKIKKkGCJFOx58uHs9P3PvzUBA4Kk9bWvGWYX9mUN7lYyaw/VubIuRu5J3xP4dUNVyznhU44TEZeRPzJBMLO07Q4i+VG0LGvSYCLedkC9JwOTqj 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: List-Subscribe: List-Unsubscribe: On Fri, Dec 13, 2024 at 07:10:43PM -0800, Luis Chamberlain wrote: Something is wrong here ... I'm just not sure what (nor am I sure why testing hasn't caught it). > - const unsigned blocks_per_page = PAGE_SIZE >> blkbits; > + const unsigned blocks_per_folio = folio_size(folio) >> blkbits; OK, fine ... > - last_block = block_in_file + args->nr_pages * blocks_per_page; > + last_block = block_in_file + args->nr_pages * blocks_per_folio; So we've scaled up the right hand side of this, that's good. > @@ -385,7 +385,7 @@ int mpage_read_folio(struct folio *folio, get_block_t get_block) > { > struct mpage_readpage_args args = { > .folio = folio, > - .nr_pages = 1, > + .nr_pages = folio_nr_pages(folio), Oh, but we've also scaled up the left hand side. So instead of being, say, 4 times larger, it's now 16 times larger. Now, where do we use it? if (block_in_file < last_block) { map_bh->b_size = (last_block-block_in_file) << blkbits; if (args->get_block(inode, block_in_file, map_bh, 0)) goto confused; so we're going to ask the filesystem for 4x as much data as we actually need. Guess it'll depend on the filesystem whether that's a bad thing or not. I guess I think the right solution here is to keep working in terms of pages. readahead_count() returns the number of pages, not the number of folios (remember we can have a mix of different size folios in the same readahead_batch). But I can be argued with.