Re: [PATCH 03/14] rbd: increase io_opt again
- To: Christoph Hellwig <hch@lst.de>
- Cc: Jens Axboe <axboe@kernel.dk>, "Martin K. Petersen" <martin.petersen@oracle.com>, Richard Weinberger <richard@nod.at>, Anton Ivanov <anton.ivanov@cambridgegreys.com>, Johannes Berg <johannes@sipsolutions.net>, Josef Bacik <josef@toxicpanda.com>, Ilya Dryomov <idryomov@gmail.com>, Dongsheng Yang <dongsheng.yang@easystack.cn>, Roger Pau Monné <roger.pau@citrix.com>, linux-um@lists.infradead.org, linux-block@vger.kernel.org, nbd@other.debian.org, ceph-devel@vger.kernel.org, xen-devel@lists.xenproject.org, linux-scsi@vger.kernel.org
- Subject: Re: [PATCH 03/14] rbd: increase io_opt again
- From: "Martin K. Petersen" <martin.petersen@oracle.com>
- Date: Thu, 13 Jun 2024 21:36:52 -0400
- Message-id: <[🔎] yq1le38tie4.fsf@ca-mkp.ca.oracle.com>
- In-reply-to: <20240531074837.1648501-4-hch@lst.de> (Christoph Hellwig's message of "Fri, 31 May 2024 09:47:58 +0200")
- References: <20240531074837.1648501-1-hch@lst.de> <20240531074837.1648501-4-hch@lst.de>
Christoph,
> Commit 16d80c54ad42 ("rbd: set io_min, io_opt and discard_granularity
> to alloc_size") lowered the io_opt size for rbd from objset_bytes
> which is 4MB for typical setup to alloc_size which is typically 64KB.
>
> The commit mostly talks about discard behavior and does mention io_min
> in passing. Reducing io_opt means reducing the readahead size, which
> seems counter-intuitive given that rbd currently abuses the user
> max_sectors setting to actually increase the I/O size. Switch back to
> the old setting to allow larger reads (the readahead size despite it's
> name actually limits the size of any buffered read) and to prepare for
> using io_opt in the max_sectors calculation and getting drivers out of
> the business of overriding the max_user_sectors value.
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
--
Martin K. Petersen Oracle Linux Engineering
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