Re: [PATCH v2] omap_hsmmc: Reduce max_segs for reliability

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On 22 June 2017 at 12:57, Will Newton <will.newton@xxxxxxxxx> wrote:
> Reduce max_segs to 64, a value that allows allocation of an entire
> EDMA descriptor list within a single page - EDMA descriptors
> are 40 bytes and the header is much larger. This avoids doing a
> higher order GFP_ATOMIC allocation in edma_prep_slave_sg
> when setting up a transfer which can potentially fail due to
> fragmentation under heavy I/O load.
>
> The current value of 1024 is unusually high in comparison to
> other mmc host drivers which mostly use values of between 1
> and 256. The EDMA driver at present splits lists above 20
> segments in any case so reducing the size of lists we pass to
> it shouldn't add much overhead.
>
> Signed-off-by: Will Newton <willn@xxxxxxxx>

Thanks, applied for next!

Kind regards
Uffe

> ---
>  drivers/mmc/host/omap_hsmmc.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> Changes in v2:
>  - More verbose commit message
>  - Rebased onto current master
>
> diff --git a/drivers/mmc/host/omap_hsmmc.c b/drivers/mmc/host/omap_hsmmc.c
> index 8c39dcc..bbcca93 100644
> --- a/drivers/mmc/host/omap_hsmmc.c
> +++ b/drivers/mmc/host/omap_hsmmc.c
> @@ -2097,9 +2097,9 @@ static int omap_hsmmc_probe(struct platform_device *pdev)
>                 host->dbclk = NULL;
>         }
>
> -       /* Since we do only SG emulation, we can have as many segs
> -        * as we want. */
> -       mmc->max_segs = 1024;
> +       /* Set this to a value that allows allocating an entire descriptor
> +        * list within a page (zero order allocation). */
> +       mmc->max_segs = 64;
>
>         mmc->max_blk_size = 512;       /* Block Length at max can be 1024 */
>         mmc->max_blk_count = 0xFFFF;    /* No. of Blocks is 16 bits */
> --
> 2.9.4
>
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