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

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Message-ID: <d1a1340a-f5f8-6953-e066-b8c6095d63fd@acm.org>
Date:   Fri, 18 Nov 2022 09:27:13 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     Adrian Hunter <adrian.hunter@...el.com>,
        Christian Löhle <CLoehle@...erstone.com>,
        "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>,
        Christoph Hellwig <hch@....de>
Cc:     Avri Altman <Avri.Altman@....com>,
        "vincent.whitchurch@...s.com" <vincent.whitchurch@...s.com>
Subject: Re: [PATCH 0/3] mmc: Improve block layer requeueing behavior

On 11/18/22 02:47, Adrian Hunter wrote:
> On 26/10/22 10:30, Christian Löhle wrote:
>> 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.
> 
> Does anyone know why the block layer does not support
> (max_hw_sectors << 9) < PAGE_SIZE ?

Hi Adrian,

Does this mean that the following patch series would not only be
useful for UFS but also for MMC? "[PATCH 00/10] Support DMA segments
smaller than the page size"
(https://lore.kernel.org/linux-block/20221019222324.362705-1-bvanassche@acm.org/).

Thanks,

Bart.