Hi Julien, From: Julien Grall <julien.grall....@gmail.com> Sent: 2021年9月27日 15:36 To: Wei Chen <wei.c...@arm.com> Cc: Stefano Stabellini <sstabell...@kernel.org>; xen-devel <xen-devel@lists.xenproject.org>; Bertrand Marquis <bertrand.marq...@arm.com>; Jan Beulich <jbeul...@suse.com>; Roger Pau Monné <roger....@citrix.com>; Andrew Cooper <andrew.coop...@citrix.com> Subject: Re: [PATCH 22/37] xen/arm: use NR_MEM_BANKS to override default NR_NODE_MEMBLKS
On Mon, 27 Sep 2021, 08:53 Wei Chen, <mailto:wei.c...@arm.com> wrote: Hi Julien, > -----Original Message----- > From: Xen-devel <mailto:xen-devel-boun...@lists.xenproject.org> On Behalf Of > Wei > Chen > Sent: 2021年9月27日 14:46 > To: Stefano Stabellini <mailto:sstabell...@kernel.org> > Cc: mailto:xen-devel@lists.xenproject.org; mailto:jul...@xen.org; Bertrand > Marquis > <mailto:bertrand.marq...@arm.com>; mailto:jbeul...@suse.com; > mailto:roger....@citrix.com; > mailto:andrew.coop...@citrix.com > Subject: RE: [PATCH 22/37] xen/arm: use NR_MEM_BANKS to override default > NR_NODE_MEMBLKS > > Hi Stefano, Julien, > > > -----Original Message----- > > From: Stefano Stabellini <mailto:sstabell...@kernel.org> > > Sent: 2021年9月27日 13:00 > > To: Wei Chen <mailto:wei.c...@arm.com> > > Cc: Stefano Stabellini <mailto:sstabell...@kernel.org>; xen- > > mailto:de...@lists.xenproject.org; mailto:jul...@xen.org; Bertrand Marquis > > <mailto:bertrand.marq...@arm.com>; mailto:jbeul...@suse.com; > > mailto:roger....@citrix.com; > > mailto:andrew.coop...@citrix.com > > Subject: RE: [PATCH 22/37] xen/arm: use NR_MEM_BANKS to override default > > NR_NODE_MEMBLKS > > > > +x86 maintainers > > > > On Mon, 27 Sep 2021, Wei Chen wrote: > > > > -----Original Message----- > > > > From: Stefano Stabellini <mailto:sstabell...@kernel.org> > > > > Sent: 2021年9月27日 11:26 > > > > To: Wei Chen <mailto:wei.c...@arm.com> > > > > Cc: Stefano Stabellini <mailto:sstabell...@kernel.org>; xen- > > > > mailto:de...@lists.xenproject.org; mailto:jul...@xen.org; Bertrand > > > > Marquis > > > > <mailto:bertrand.marq...@arm.com> > > > > 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 <mailto:sstabell...@kernel.org> > > > > > > Sent: 2021年9月24日 9:35 > > > > > > To: Wei Chen <mailto:wei.c...@arm.com> > > > > > > Cc: mailto:xen-devel@lists.xenproject.org; > > > > > > mailto:sstabell...@kernel.org; > > > > mailto:jul...@xen.org; > > > > > > Bertrand Marquis <mailto: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. > > > > > > > > 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 <mailto: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 > > > > > > > > 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? > > > > Yes. > > > 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? > > > > At that time, this was probably the most cost-effective approach. > Enough and easy. But, if more nodes need to be supported in the > future, it may bring more memory blocks. And this maximum value > might not apply. The maximum may need to support dynamic extension. > > > > > 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: > > > > Probably not, NR_MEM_BANKS will count those memory ranges without > numa-node-id in boot memory parsing stage (process_memory_node or > EFI parser). But NR_NODE_MEMBLKS will only count those memory ranges > with numa-node-id. > > > #define NR_NODE_MEMBLKS MAX(NR_MEM_BANKS, (CONFIG_NR_NUMA_NODES * 2)) > > > > > Quote Julien's comment from HTML email to here: > " 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. > " > > > But here comes the problem: > > How can we set the NR_MEM_BANKS maximum value, 128 seems an arbitrary too? > > This is based on hardware we currently support (the last time we bumped the > value was, IIRC, for Thunder-X). In the case of booting UEFI, we can get a > lot of small ranges as we discover the RAM using the UEFI memory map. > Thanks for the background. > > > If #define NR_MEM_BANKS (CONFIG_NR_NUMA_NODES * N)? And what N should be. > > N would have to be the maximum number of ranges you can find in a NUMA node. > > We would also need to make sure this doesn't break existing platforms. So N > would have to be quite large or we need a MAX as Stefano suggested. > > But I would prefer to keep the existing 128 and allow to configure it at > build time (not necessarily in this series). This avoid to have different way > to define the value based NUMA vs non-NUMA. In this case, can we use Stefano's "#define NR_NODE_MEMBLKS MAX(NR_MEM_BANKS, (CONFIG_NR_NUMA_NODES * 2))" in next version. If yes, should we change x86 part? Because NR_MEM_BANKS has not been defined in x86. > > And maybe the definition could be common with x86 if we define > > NR_MEM_BANKS to 128 on x86 too. > > Julien had comment here, I will continue in that email.
