Re: [PATCH 14/15] x86/numa: remove redundant iteration over memblock.reserved

Mike Rapoport
2020-07-28T14:15:24Z

On Tue, Jul 28, 2020 at 07:02:54PM +0800, Baoquan He wrote:
> On 07/28/20 at 08:11am, Mike Rapoport wrote:
> > From: Mike Rapoport <rppt@linux.ibm.com>
> >
> > numa_clear_kernel_node_hotplug() function first traverses numa_meminfo
> > regions to set node ID in memblock.reserved and than traverses
> > memblock.reserved to update reserved_nodemask to include node IDs that were
> > set in the first loop.
> >
> > Remove redundant traversal over memblock.reserved and update
> > reserved_nodemask while iterating over numa_meminfo.
> >
> > Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> > ---
> > arch/x86/mm/numa.c | 26 ++++++++++----------------
> > 1 file changed, 10 insertions(+), 16 deletions(-)
> >
> > diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
> > index 8ee952038c80..4078abd33938 100644
> > --- a/arch/x86/mm/numa.c
> > +++ b/arch/x86/mm/numa.c
> > @@ -498,31 +498,25 @@ static void __init numa_clear_kernel_node_hotplug(void)
> > * and use those ranges to set the nid in memblock.reserved.
> > * This will split up the memblock regions along node
> > * boundaries and will set the node IDs as well.
> > + *
> > + * The nid will also be set in reserved_nodemask which is later
> > + * used to clear MEMBLOCK_HOTPLUG flag.
> > + *
> > + * [ Note, when booting with mem=nn[kMG] or in a kdump kernel,
> > + * numa_meminfo might not include all memblock.reserved
> > + * memory ranges, because quirks such as trim_snb_memory()
> > + * reserve specific pages for Sandy Bridge graphics.
> > + * These ranges will remain with nid == MAX_NUMNODES. ]
> > */
> > for (i = 0; i < numa_meminfo.nr_blks; i++) {
> > struct numa_memblk *mb = numa_meminfo.blk + i;
> > int ret;
> >
> > ret = memblock_set_node(mb->start, mb->end - mb->start, &memblock.reserved, mb->nid);
> > + node_set(mb->nid, reserved_nodemask);
>
> Really? This will set all node id into reserved_nodemask. But in the
> current code, it's setting nid into memblock reserved region which
> interleaves with numa_memoinfo, then get those nid and set it in
> reserved_nodemask. This is so different, with my understanding. Please
> correct me if I am wrong.

You are right, I've missed the intersections of numa_meminfo with
memblock.reserved.

x86 interaction with membock is so, hmm, interesting...

> Thanks
> Baoquan
>
> > WARN_ON_ONCE(ret);
> > }
> >
> > - /*
> > - * Now go over all reserved memblock regions, to construct a
> > - * node mask of all kernel reserved memory areas.
> > - *
> > - * [ Note, when booting with mem=nn[kMG] or in a kdump kernel,
> > - * numa_meminfo might not include all memblock.reserved
> > - * memory ranges, because quirks such as trim_snb_memory()
> > - * reserve specific pages for Sandy Bridge graphics. ]
> > - */
> > - for_each_memblock(reserved, mb_region) {
> > - int nid = memblock_get_region_node(mb_region);
> > -
> > - if (nid != MAX_NUMNODES)
> > - node_set(nid, reserved_nodemask);
> > - }
> > -
> > /*
> > * Finally, clear the MEMBLOCK_HOTPLUG flag for all memory
> > * belonging to the reserved node mask.
> > --
> > 2.26.2
> >
> >
>

--
Sincerely yours,
Mike.