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Thu, 13 Mar 2025 08:34:39 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id U8wfLp+Y0mfWJwAAD6G6ig (envelope-from ); Thu, 13 Mar 2025 08:34:39 +0000 Message-ID: <17f4795a-f6c8-4e6c-ba31-c65eab18efd1@suse.de> Date: Thu, 13 Mar 2025 09:34:39 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: Decline to manipulate the refcount on a slab page To: Christoph Hellwig Cc: Matthew Wilcox , Jakub Kicinski , Andrew Morton , netdev@vger.kernel.org, Vlastimil Babka , linux-mm@kvack.org References: <20250310143544.1216127-1-willy@infradead.org> <20250311111511.2531b260@kernel.org> <4fc21641-e258-474b-9409-4949fe2fda2d@suse.de> <9af6dff3-adce-40f8-8649-282212acad9e@suse.de> Content-Language: en-US From: Hannes Reinecke In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: ED158100005 X-Stat-Signature: 1m9itdeb7hqn3rk1rnuk1dxpyz4ih5m4 X-HE-Tag: 1741854881-533913 X-HE-Meta: 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 QlZa/gee j8pv/cBDO+wpDx6F8dm/FM6whi/cc/QB8XqgLZ1omdGBfAOVl24DM52lGcwTxlpkXobtzNpIdZ7BUkgsbNFEVc9RuV8aZbLnTwFYMdhFT9TfeOL3GHaOIk7/JW2MGer8TLaKAHeZh5JJz0A6WwQFXzAmHSEYk8LqjFgEF3hTfAf1FaS2b/YaDmXtkuYZzyyNafMCrKCq7BEEsRWZN/xDMdOicLfJgS2XoSij7aDaz7B9q+uSLt4SVZM9XyVnvhT8HXpYHTQHlM71IE8Ur2GtCRNrF2Siss1SkiKe8B5WD0uZty1WM6DLu07+FhwhoH9Tn7hWXo288+NAxdro= 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 3/13/25 08:36, Christoph Hellwig wrote: > On Thu, Mar 13, 2025 at 08:22:01AM +0100, Hannes Reinecke wrote: >> On 3/12/25 06:48, Christoph Hellwig wrote: >>> On Tue, Mar 11, 2025 at 04:59:53PM +0000, Matthew Wilcox wrote: >>>> So I have two questions: >>>> >>>> Hannes: >>>> - Why does nvme need to turn the kvec into a bio rather than just >>>> send it directly? >>> >>> It doensn't need to and in fact does not. >>> >> Errm ... nvmf_connect_admin_queue()/nvmf_connect_io_queue() does ... > > No kvec there. Just plain old passthrough commands like many others. I might be misunderstood. nvmf_connect_command_prep() returns a kmalloced buffer. That is stored in a bvec in _nvme_submit_sync_cmd() via blk_mq_rq_map_kern()->bio_map_kern(). And from that point on we are dealing with bvecs (iterators and all), and losing the information that the page referenced is a slab page. The argument is that the network layer expected a kvec iterator when slab pages are referred to, not a bvec iterator. Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich