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

Baoquan He
2020-07-28T11:03:16Z

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.

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