Re: [Xen-devel] [PATCH v2] mm/page_alloc: fix MEMF_no_dma allocations for single NUMA

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.01.19 at 16:45, <sergey.dyasli@xxxxxxxxxx> wrote:
> Currently dma_bitsize is zero by default on single NUMA node machines.
> This makes all alloc_domheap_pages() calls with MEMF_no_dma return NULL.
> 
> There is only 1 user of MEMF_no_dma: dom0_memflags, which are used
> during memory allocation for Dom0. Failing allocation with default
> dom0_memflags is especially severe for the PV Dom0 case: it makes
> alloc_chunk() to use suboptimal 2MB allocation algorithm with a search
> for higher memory addresses.
> 
> This can lead to the NMI watchdog timeout during PV Dom0 construction
> on some machines, which can be worked around by specifying "dma_bits"
> in Xen's cmdline manually.
> 
> Fix the issue by ignoring MEMF_no_dma in cases when dma_bitsize is zero,
> which means there is no DMA zone. This shouldn't cause any issues for
> Dom0 because alloc_heap_pages() will first use higher memory addresses
> for satisfying memory allocation requests.
> 
> Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
(could also be Suggested-by)

Jan



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