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Wed, 10 Apr 2024 08:34:43 +0000 Received: from DM6PR10MB4313.namprd10.prod.outlook.com ([fe80::ae68:7d51:133f:324]) by DM6PR10MB4313.namprd10.prod.outlook.com ([fe80::ae68:7d51:133f:324%4]) with mapi id 15.20.7409.042; Wed, 10 Apr 2024 08:34:43 +0000 Message-ID: Date: Wed, 10 Apr 2024 09:34:36 +0100 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 00/10] block atomic writes To: Luis Chamberlain Cc: Matthew Wilcox , Pankaj Raghav , Daniel Gomez , =?UTF-8?Q?Javier_Gonz=C3=A1lez?= , axboe@kernel.dk, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me, jejb@linux.ibm.com, martin.petersen@oracle.com, djwong@kernel.org, viro@zeniv.linux.org.uk, brauner@kernel.org, dchinner@redhat.com, jack@suse.cz, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-fsdevel@vger.kernel.org, tytso@mit.edu, jbongio@google.com, linux-scsi@vger.kernel.org, ojaswin@linux.ibm.com, linux-aio@kvack.org, linux-btrfs@vger.kernel.org, io-uring@vger.kernel.org, nilay@linux.ibm.com, ritesh.list@gmail.com References: <20240326133813.3224593-1-john.g.garry@oracle.com> Content-Language: en-US From: John Garry Organization: Oracle Corporation In-Reply-To: Content-Type: text/plain; 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But when you > use a 16k sector size, the 16k IOs should be respected by the > filesystem. > > Do we break BIOs to below a min order if the sector size is also set to > 16k? I haven't seen that and its unclear when or how that could happen. AFAICS, the only guarantee is to not split below LBS. > > At least for NVMe we don't need to yell to a device to inform it we want > a 16k IO issued to it to be atomic, if we read that it has the > capability for it, it just does it. The IO verificaiton can be done with > blkalgn [0]. > > Does SCSI*require* an 16k atomic prep work, or can it be done implicitly? > Does it need WRITE_ATOMIC_16? physical block size is what we can implicitly write atomically. So if you have a 4K PBS and 512B LBS, then WRITE_ATOMIC_16 would be required to write 16KB atomically. > > [0]https://urldefense.com/v3/__https://github.com/dagmcr/bcc/tree/blkalgn__;!!ACWV5N9M2RV99hQ!I0tfdPsEq9vdHMSC7JVmVDHCb5w6invjudW7pZW50v3mZ7dWMMf0cBtY_BQlZZmYSjLzPQDZoLO7-K6MQQ$ > >> So just increasing the inode block size / FS block size does not >> really change anything, in itself. > If we're breaking up IOs when a min order is set for an inode, that > would need to be looked into, but we're not seeing that. In practice you won't see it, but I am talking about guarantees not to see it. > >>> Do untorn writes actually exist in SCSI? I was under the impression >>> nobody had actually implemented them in SCSI hardware. >> I know that some SCSI targets actually atomically write data in chunks > >> LBS. Obviously atomic vs non-atomic performance is a moot point there, as >> data is implicitly always atomically written. >> >> We actually have an mysql/innodb port of this API working on such a SCSI >> target. > I suspect IO verification with the above tool should prove to show the > same if you use a filesystem with a larger sector size set too, and you > just would not have to do any changes to userspace other than the > filesystem creation with say mkfs.xfs params of -b size=16k -s size=16k Ok, I see > >> However I am not sure about atomic write support for other SCSI targets. > Good to know! > >>>> We saw untorn writes as not being a property of the file or even the inode >>>> itself, but rather an attribute of the specific IO being issued from the >>>> userspace application. >>> The problem is that keeping track of that is expensive for buffered >>> writes. It's a model that only works for direct IO. Arguably we >>> could make it work for O_SYNC buffered IO, but that'll require some >>> surgery. >> To me, O_ATOMIC would be required for buffered atomic writes IO, as we want >> a fixed-sized IO, so that would mean no mixing of atomic and non-atomic IO. > Would using the same min and max order for the inode work instead? Maybe, I would need to check further. Thanks, John