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Re: [PATCH 03/14] rbd: increase io_opt again
- To: Christoph Hellwig <hch@xxxxxx>
- From: "Martin K. Petersen" <martin.petersen@xxxxxxxxxx>
- Date: Thu, 13 Jun 2024 21:36:52 -0400
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- Cc: Jens Axboe <axboe@xxxxxxxxx>, "Martin K. Petersen" <martin.petersen@xxxxxxxxxx>, Richard Weinberger <richard@xxxxxx>, Anton Ivanov <anton.ivanov@xxxxxxxxxxxxxxxxxx>, Johannes Berg <johannes@xxxxxxxxxxxxxxxx>, Josef Bacik <josef@xxxxxxxxxxxxxx>, Ilya Dryomov <idryomov@xxxxxxxxx>, Dongsheng Yang <dongsheng.yang@xxxxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, linux-um@xxxxxxxxxxxxxxxxxxx, linux-block@xxxxxxxxxxxxxxx, nbd@xxxxxxxxxxxxxxxx, ceph-devel@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-scsi@xxxxxxxxxxxxxxx
- Delivery-date: Fri, 14 Jun 2024 01:37:17 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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@xxxxxxxxxx>
--
Martin K. Petersen Oracle Linux Engineering
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