On Mon, 27 Sep 2021, 06:59 Stefano Stabellini, <[email protected]> wrote:
> +x86 maintainers > > On Mon, 27 Sep 2021, Wei Chen wrote: > > > -----Original Message----- > > > From: Stefano Stabellini <[email protected]> > > > Sent: 2021年9月27日 11:26 > > > To: Wei Chen <[email protected]> > > > Cc: Stefano Stabellini <[email protected]>; xen- > > > [email protected]; [email protected]; Bertrand Marquis > > > <[email protected]> > > > Subject: RE: [PATCH 22/37] xen/arm: use NR_MEM_BANKS to override > default > > > NR_NODE_MEMBLKS > > > > > > On Sun, 26 Sep 2021, Wei Chen wrote: > > > > > -----Original Message----- > > > > > From: Stefano Stabellini <[email protected]> > > > > > Sent: 2021年9月24日 9:35 > > > > > To: Wei Chen <[email protected]> > > > > > Cc: [email protected]; [email protected]; > > > [email protected]; > > > > > Bertrand Marquis <[email protected]> > > > > > 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. > > > > > > OK. In that case I'd say to get rid of the previous definition of > > > NR_NODE_MEMBLKS as it is probably not necessary, see below. > > > > > > > > > > > > > > > > > > > > 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 <[email protected]> > > > > > > --- > > > > > > 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 > > > > > > This one we can remove it completely right? > > > > How about define NR_MEM_BANKS to: > > #ifdef CONFIG_NR_NUMA_NODES > > #define NR_MEM_BANKS (CONFIG_NR_NUMA_NODES * 2) > > #else > > #define NR_MEM_BANKS 128 > > #endif > > for both x86 and Arm. For those architectures do not support or enable > > NUMA, they can still use "NR_MEM_BANKS 128". And replace all > NR_NODE_MEMBLKS > > in NUMA code to NR_MEM_BANKS to remove NR_NODE_MEMBLKS completely. > > In this case, NR_MEM_BANKS can be aware of the changes of > CONFIG_NR_NUMA_NODES. > > x86 doesn't have NR_MEM_BANKS as far as I can tell. I guess you also > meant to rename NR_NODE_MEMBLKS to NR_MEM_BANKS? > > But NR_MEM_BANKS is not directly related to CONFIG_NR_NUMA_NODES because > there can be many memory banks for each numa node, certainly more than > 2. The existing definition on x86: > > #define NR_NODE_MEMBLKS (MAX_NUMNODES*2) > > Doesn't make a lot of sense to me. Was it just an arbitrary limit for > the lack of a better way to set a maximum? > > > On the other hand, NR_MEM_BANKS and NR_NODE_MEMBLKS seem to be related. > In fact, what's the difference? > > NR_MEM_BANKS is the max number of memory banks (with or without > numa-node-id). > > NR_NODE_MEMBLKS is the max number of memory banks with NUMA support > (with numa-node-id)? > > They are basically the same thing. On ARM I would just do: > > #define NR_NODE_MEMBLKS MAX(NR_MEM_BANKS, (CONFIG_NR_NUMA_NODES * 2)) > As you wrote above, the second part of the MAX is totally arbitrary. In fact, it is very likely than if you have more than 64 nodes, you may need a lot more than 2 regions per node. So, for Arm, I would just define NR_NODE_MEMBLKS as an alias to NR_MEM_BANKS so it can be used by common code.
