Hi Stefano, > -----Original Message----- > From: Stefano Stabellini <sstabell...@kernel.org> > Sent: 2021年9月24日 9:35 > To: Wei Chen <wei.c...@arm.com> > Cc: xen-devel@lists.xenproject.org; sstabell...@kernel.org; jul...@xen.org; > Bertrand Marquis <bertrand.marq...@arm.com> > Subject: Re: [PATCH 22/37] xen/arm: use NR_MEM_BANKS to override default > NR_NODE_MEMBLKS > > On Thu, 23 Sep 2021, Wei Chen wrote: > > As a memory range described in device tree cannot be split across > > multiple nodes. So we define NR_NODE_MEMBLKS as NR_MEM_BANKS in > > arch header. > > This statement is true but what is the goal of this patch? Is it to > reduce code size and memory consumption? >
No, when Julien and I discussed this in last version[1], we hadn't thought so deeply. We just thought a memory range described in DT cannot be split across multiple nodes. So NR_MEM_BANKS should be equal to NR_MEM_BANKS. https://lists.xenproject.org/archives/html/xen-devel/2021-08/msg00974.html > I am asking because NR_MEM_BANKS is 128 and > NR_NODE_MEMBLKS=2*MAX_NUMNODES which is 64 by default so again > NR_NODE_MEMBLKS is 128 before this patch. > > In other words, this patch alone doesn't make any difference; at least > doesn't make any difference unless CONFIG_NR_NUMA_NODES is increased. > > So, is the goal to reduce memory usage when CONFIG_NR_NUMA_NODES is > higher than 64? > I also thought about this problem when I was writing this patch. CONFIG_NR_NUMA_NODES is increasing, but NR_MEM_BANKS is a fixed value, then NR_MEM_BANKS can be smaller than CONFIG_NR_NUMA_NODES at one point. But I agree with Julien's suggestion, NR_MEM_BANKS and NR_NODE_MEMBLKS must be aware of each other. I had thought to add some ASSERT check, but I don't know how to do it better. So I post this patch for more suggestion. > > > And keep default NR_NODE_MEMBLKS in common header > > for those architectures NUMA is disabled. > > This last sentence is not accurate: on x86 NUMA is enabled and > NR_NODE_MEMBLKS is still defined in xen/include/xen/numa.h (there is no > x86 definition of it) > Yes. > > > Signed-off-by: Wei Chen <wei.c...@arm.com> > > --- > > xen/include/asm-arm/numa.h | 8 +++++++- > > xen/include/xen/numa.h | 2 ++ > > 2 files changed, 9 insertions(+), 1 deletion(-) > > > > diff --git a/xen/include/asm-arm/numa.h b/xen/include/asm-arm/numa.h > > index 8f1c67e3eb..21569e634b 100644 > > --- a/xen/include/asm-arm/numa.h > > +++ b/xen/include/asm-arm/numa.h > > @@ -3,9 +3,15 @@ > > > > #include <xen/mm.h> > > > > +#include <asm/setup.h> > > + > > typedef u8 nodeid_t; > > > > -#ifndef CONFIG_NUMA > > +#ifdef CONFIG_NUMA > > + > > +#define NR_NODE_MEMBLKS NR_MEM_BANKS > > + > > +#else > > > > /* Fake one node for now. See also node_online_map. */ > > #define cpu_to_node(cpu) 0 > > diff --git a/xen/include/xen/numa.h b/xen/include/xen/numa.h > > index 1978e2be1b..1731e1cc6b 100644 > > --- a/xen/include/xen/numa.h > > +++ b/xen/include/xen/numa.h > > @@ -12,7 +12,9 @@ > > #define MAX_NUMNODES 1 > > #endif > > > > +#ifndef NR_NODE_MEMBLKS > > #define NR_NODE_MEMBLKS (MAX_NUMNODES*2) > > +#endif > > > > #define vcpu_to_node(v) (cpu_to_node((v)->processor)) > > > > -- > > 2.25.1 > >
