Re: [PATCHv2 1/7] x86/mm: concentrate the code to memblock allocator enabled

[Pingfan Liu <kernelfans@gmail.com>]

On Fri, Jan 11, 2019 at 2:13 PM Chao Fan <fanc.fnst@cn.fujitsu.com> wrote:
>
> On Fri, Jan 11, 2019 at 01:12:51PM +0800, Pingfan Liu wrote:
> >This patch identifies the point where memblock alloc start. It has no
> >functional.
> [...]
> >+#ifdef CONFIG_MEMORY_HOTPLUG
> >+      /*
> >+       * Memory used by the kernel cannot be hot-removed because Linux
> >+       * cannot migrate the kernel pages. When memory hotplug is
> >+       * enabled, we should prevent memblock from allocating memory
> >+       * for the kernel.
> >+       *
> >+       * ACPI SRAT records all hotpluggable memory ranges. But before
> >+       * SRAT is parsed, we don't know about it.
> >+       *
> >+       * The kernel image is loaded into memory at very early time. We
> >+       * cannot prevent this anyway. So on NUMA system, we set any
> >+       * node the kernel resides in as un-hotpluggable.
> >+       *
> >+       * Since on modern servers, one node could have double-digit
> >+       * gigabytes memory, we can assume the memory around the kernel
> >+       * image is also un-hotpluggable. So before SRAT is parsed, just
> >+       * allocate memory near the kernel image to try the best to keep
> >+       * the kernel away from hotpluggable memory.
> >+       */
> >+      if (movable_node_is_enabled())
> >+              memblock_set_bottom_up(true);
>
> Hi Pingfan,
>
> In my understanding, 'movable_node' is based on the that memory near
> kernel is considered as in the same node as kernel in high possibility.
>
> If SRAT has been parsed early, do we still need the kernel parameter
> 'movable_node'? Since you have got the memory information about hot-remove,
> so I wonder if it's OK to drop 'movable_node', and if memory-hotremove is
> enabled, change memblock allocation according to SRAT.
>
x86_32 still need this logic. Maybe it can be doable later.

Thanks,
Pingfan
> If there is something wrong in my understanding, please let me know.
>
> Thanks,
> Chao Fan
>
> >+#endif
> >       init_mem_mapping();
> >+      memblock_set_current_limit(get_max_mapped());
> >
> >       idt_setup_early_pf();
> >
> >@@ -1145,8 +1145,6 @@ void __init setup_arch(char **cmdline_p)
> >        */
> >       mmu_cr4_features = __read_cr4() & ~X86_CR4_PCIDE;
> >
> >-      memblock_set_current_limit(get_max_mapped());
> >-
> >       /*
> >        * NOTE: On x86-32, only from this point on, fixmaps are ready for use.
> >        */
> >--
> >2.7.4
> >
> >
> >
>
>