> -----Original Message-----
> From: Song Bao Hua (Barry Song)
> Sent: Saturday, August 22, 2020 7:27 AM
> To: 'Mike Kravetz' <mike.krav...@oracle.com>; h...@lst.de;
> m.szyprow...@samsung.com; robin.mur...@arm.com; w...@kernel.org;
> ganapatrao.kulka...@cavium.com; catalin.mari...@arm.com;
> a...@linux-foundation.org
> Cc: io...@lists.linux-foundation.org; linux-arm-ker...@lists.infradead.org;
> linux-kernel@vger.kernel.org; Zengtao (B) <prime.z...@hisilicon.com>;
> huangdaode <huangda...@huawei.com>; Linuxarm <linux...@huawei.com>
> Subject: RE: [PATCH v7 0/3] make dma_alloc_coherent NUMA-aware by
> per-NUMA CMA
>
>
>
> > -----Original Message-----
> > From: Mike Kravetz [mailto:mike.krav...@oracle.com]
> > Sent: Saturday, August 22, 2020 5:53 AM
> > To: Song Bao Hua (Barry Song) <song.bao....@hisilicon.com>; h...@lst.de;
> > m.szyprow...@samsung.com; robin.mur...@arm.com; w...@kernel.org;
> > ganapatrao.kulka...@cavium.com; catalin.mari...@arm.com;
> > a...@linux-foundation.org
> > Cc: io...@lists.linux-foundation.org; linux-arm-ker...@lists.infradead.org;
> > linux-kernel@vger.kernel.org; Zengtao (B) <prime.z...@hisilicon.com>;
> > huangdaode <huangda...@huawei.com>; Linuxarm
> <linux...@huawei.com>
> > Subject: Re: [PATCH v7 0/3] make dma_alloc_coherent NUMA-aware by
> > per-NUMA CMA
> >
> > Hi Barry,
> > Sorry for jumping in so late.
> >
> > On 8/21/20 4:33 AM, Barry Song wrote:
> > >
> > > with per-numa CMA, smmu will get memory from local numa node to save
> > command
> > > queues and page tables. that means dma_unmap latency will be shrunk
> > much.
> >
> > Since per-node CMA areas for hugetlb was introduced, I have been thinking
> > about the limited number of CMA areas. In most configurations, I believe
> > it is limited to 7. And, IIRC it is not something that can be changed at
> > runtime, you need to reconfig and rebuild to increase the number. In
> contrast
> > some configs have NODES_SHIFT set to 10. I wasn't too worried because of
> > the limited hugetlb use case. However, this series is adding another user
> > of per-node CMA areas.
> >
> > With more users, should try to sync up number of CMA areas and number of
> > nodes? Or, perhaps I am worrying about nothing?
>
> Hi Mike,
> The current limitation is 8. If the server has 4 nodes and we enable both
> pernuma
> CMA and hugetlb, the last node will fail to get one cma area as the default
> global cma area will take 1 of 8. So users need to change menuconfig.
> If the server has 8 nodes, we enable one of pernuma cma and hugetlb, one
> node
> will fail to get cma.
>
> We may set the default number of CMA areas as 8+MAX_NODES(if hugetlb
> enabled) +
> MAX_NODES(if pernuma cma enabled) if we don't expect users to change
> config, but
> right now hugetlb has not an option in Kconfig to enable or disable like
> pernuma cma
> has DMA_PERNUMA_CMA.
I would prefer we make some changes like:
config CMA_AREAS
int "Maximum count of the CMA areas"
depends on CMA
+ default 19 if NUMA
default 7
help
CMA allows to create CMA areas for particular purpose, mainly,
used as device private area. This parameter sets the maximum
number of CMA area in the system.
- If unsure, leave the default value "7".
+ If unsure, leave the default value "7" or "19" if NUMA is used.
1+ CONFIG_CMA_AREAS should be quite enough for almost all servers in the
markets.
If 2 numa nodes, and both hugetlb cma and pernuma cma is enabled, we need 2*2 +
1 = 5
If 4 numa nodes, and both hugetlb cma and pernuma cma is enabled, we need 2*4 +
1 = 9 -> default ARM64 config.
If 8 numa nodes, and both hugetlb cma and pernuma cma is enabled, we need 2*8 +
1 = 17
The default value is supporting the most common case and is not going to
support those servers
with NODES_SHIFT=10, they can make their own config just like users need to
increase CMA_AREAS
if they add many cma areas in device tree in a system even without NUMA.
How do you think, mike?
Thanks
Barry
