Re: + x86-vmemmap-handle-unpopulated-sub-pmd-ranges.patch added to -mm tree

[Oscar Salvador <osalvador@suse.de>]

On Wed, Mar 10, 2021 at 02:58:56PM -0800, akpm@linux-foundation.org wrote:
> ------------------------------------------------------
> From: Oscar Salvador <osalvador@suse.de>
> Subject: x86/vmemmap: handle unpopulated sub-pmd ranges
> 
> When sizeof(struct page) is not a power of 2, sections do not span a PMD
> anymore and so when populating them some parts of the PMD will remain
> unused.
> 
> Because of this, PMDs will be left behind when depopulating sections since
> remove_pmd_table() thinks that those unused parts are still in use.
> 
> Fix this by marking the unused parts with PAGE_UNUSED, so memchr_inv()
> will do the right thing and will let us free the PMD when the last user of
> it is gone.
> 
> This patch is based on a similar patch by David Hildenbrand:
> 
> https://lore.kernel.org/linux-mm/20200722094558.9828-9-david@redhat.com/
> 
> Link: https://lkml.kernel.org/r/20210309214050.4674-4-osalvador@suse.de
> Signed-off-by: Oscar Salvador <osalvador@suse.de>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: "H . Peter Anvin" <hpa@zytor.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Zi Yan <ziy@nvidia.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Hi Andrew,

Could you squash the following on top?
It seems that we need to go back to the ifdef version as the IS_ENABLED
does not properly work and throws a warning.

Thanks a lot

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 13187a3debe9..bbef99622370 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1123,15 +1123,16 @@ remove_pmd_table(pmd_t *pmd_start, unsigned long addr, unsigned long end,
 				pmd_clear(pmd);
 				spin_unlock(&init_mm.page_table_lock);
 				pages++;
-			} else if (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) &&
-				   vmemmap_pmd_is_unused(addr, next)) {
+			}
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+			else if (vmemmap_pmd_is_unused(addr, next)) {
 					free_hugepage_table(pmd_page(*pmd),
 							    altmap);
 					spin_lock(&init_mm.page_table_lock);
 					pmd_clear(pmd);
 					spin_unlock(&init_mm.page_table_lock);
 			}
-
+#endif
 			continue;
 		}




-- 
Oscar Salvador
SUSE L3