linux-kernel - Re: [PATCH v2] dma-pool: Fix too large DMA pools on medium systems

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Message-ID: <20200620200936.GA106151@roeck-us.net>
Date:   Sat, 20 Jun 2020 13:09:36 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        David Rientjes <rientjes@...gle.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] dma-pool: Fix too large DMA pools on medium systems

On Mon, Jun 08, 2020 at 03:22:17PM +0200, Geert Uytterhoeven wrote:
> On systems with at least 32 MiB, but less than 32 GiB of RAM, the DMA
> memory pools are much larger than intended (e.g. 2 MiB instead of 128
> KiB on a 256 MiB system).
> 
> Fix this by correcting the calculation of the number of GiBs of RAM in
> the system.  Invert the order of the min/max operations, to keep on
> calculating in pages until the last step, which aids readability.
> 
> Fixes: 1d659236fb43c4d2 ("dma-pool: scale the default DMA coherent pool size with memory capacity")
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> Acked-by: David Rientjes <rientjes@...gle.com>

This patch results in a boot failure in some of my powerpc boot tests,
specifically those testing boots from mptsas1068 devices. Error message:

mptsas 0000:00:02.0: enabling device (0000 -> 0002)
mptbase: ioc0: Initiating bringup
ioc0: LSISAS1068 A0: Capabilities={Initiator}
mptbase: ioc0: ERROR - Unable to allocate Reply, Request, Chain Buffers!
mptbase: ioc0: ERROR - didn't initialize properly! (-3)
mptsas: probe of 0000:00:02.0 failed with error -3

Configuration is bamboo:44x/bamboo_defconfig plus various added drivers.
Qemu command line is

qemu-system-ppc -kernel vmlinux -M bamboo \
     -m 256 -no-reboot -snapshot -device mptsas1068,id=scsi \
     -device scsi-hd,bus=scsi.0,drive=d0,wwn=0x5000c50015ea71ac -drive \
     file=rootfs.ext2,format=raw,if=none,id=d0 \
     --append "panic=-1 slub_debug=FZPUA root=/dev/sda  mem=256M console=ttyS0" \
     -monitor none -nographic

canyonlands_defconfig with sam460ex machine and otherwise similar command line
fails as well.

Reverting this patch fixes the problem.

Guenter