Re: [PATCHv2 1/7] x86/mm: concentrate the code to memblock allocator enabled
- Date: Fri, 11 Jan 2019 18:06:55 +0800
- From: Pingfan Liu <kernelfans@xxxxxxxxx>
- Subject: Re: [PATCHv2 1/7] x86/mm: concentrate the code to memblock allocator enabled
On Fri, Jan 11, 2019 at 2:13 PM Chao Fan <fanc.fnst@xxxxxxxxxxxxxx> 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
> >+#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.
> If there is something wrong in my understanding, please let me know.
> Chao Fan
> > 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.
> > */