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SubjectRe: [PATCH] Fix memory hotplug and bouncing in block layer

Oh, thanks for your fixing.

Acked-by: Yasunori Goto <y-goto@jp.fujitsu.com>


> Fix memory hotplug and bouncing in block layer
>
> Only noticed this while hacking something else, no test case.
>
> blk_max_low_pfn is initialized once at bootup by the block layer
> from max_low_pfn. But max_low_pfn is not necessarily constant
> over the runtime of the system when you consider memory hotplug.
> What could happen if that someone adds memory later the block
> layer wouldn't get updated and then start bouncing memory unnecessarily.
>
> Also on 64bit blk_max_low_pfn actually isn't needed because
> it just disables bouncing essentially and there is no highmem.
> And nobody can pass pfns > max_low_pfn to the block layer,
> because those wouldn't have a struct page and I suspect
> block layer wouldn't be very happy without that.
>
> So set BLK_BOUNCE_HIGH to infinity (-1ULL) on 64bit. That
> avoids the problem of having to update it on memory hotadd.
>
> On 32bit I kept the same behaviour because at least on i386
> memory hotadd only adds HIGHMEM, never lowmem.
>
> BLK_BOUNCE_ANY is always set to infinity on both 32 and 64bit.
>
> Signed-off-by: Andi Kleen <ak@suse.de>
>
> ---
> include/linux/blkdev.h | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> Index: linux/include/linux/blkdev.h
> ===================================================================
> --- linux.orig/include/linux/blkdev.h
> +++ linux/include/linux/blkdev.h
> @@ -532,8 +532,13 @@ extern unsigned long blk_max_low_pfn, bl
> * BLK_BOUNCE_ANY : don't bounce anything
> * BLK_BOUNCE_ISA : bounce pages above ISA DMA boundary
> */
> +
> +#if BITS_PER_LONG == 32
> #define BLK_BOUNCE_HIGH ((u64)blk_max_low_pfn << PAGE_SHIFT)
> -#define BLK_BOUNCE_ANY ((u64)blk_max_pfn << PAGE_SHIFT)
> +#else
> +#define BLK_BOUNCE_HIGH -1ULL
> +#endif
> +#define BLK_BOUNCE_ANY (-1ULL)
> #define BLK_BOUNCE_ISA (ISA_DMA_THRESHOLD)

--
Yasunori Goto




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