linux-kernel - [PATCH 0/3] mmc: Improve block layer requeueing behavior

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Date:   Wed, 26 Oct 2022 07:30:37 +0000
From:   Christian Löhle <CLoehle@...erstone.com>
To:     "axboe@...nel.dk" <axboe@...nel.dk>,
        "ulf.hansson@...aro.org" <ulf.hansson@...aro.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>
CC:     Avri Altman <Avri.Altman@....com>,
        "adrian.hunter@...el.com" <adrian.hunter@...el.com>,
        "vincent.whitchurch@...s.com" <vincent.whitchurch@...s.com>,
        Christian Löhle <CLoehle@...erstone.com>
Subject: [PATCH 0/3] mmc: Improve block layer requeueing behavior

Mmcblk relies on block layer requeueing to fulfill some requests under
certain conditions. Improve the handling to get nicely ordered requests.

Using the terms a bit loosely to get a point across:
Current behavior for 512 blksz and max_blk_count = 1 the scenario would
be as follows:

- request for page 0 lba 0 to 7
- request for page 1 lba 8 to 15
- request for page 2 lba 16 to 23
- request for page 3 lba 24 to 31

mmcblk modifies data->blocks = 1 for each and requeues,
this leads to:

Access lba 0
Access lba 8
Access lba 16
Access lba 24
Access lba 1 (1. Requeue for page 0)
Access lba 9 (1. Requeue for page 1)
Access lba 17 (1. Requeue for page 2)
Access lba 25 (1. Requeue for page 3)
Access lba 2 (2. Requeue for page 0)
...

Of course we would rather have lbas consecutive.
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