x86/mm/hotplug: Don't remove PGD entries in remove_pagetable()

Ingo Molnar · Ingo Molnar · commit af2cf278ef4f · 2016-07-15T10:26:24.000+02:00
So when memory hotplug removes a piece of physical memory from pagetable mappings, it also frees the underlying PGD entry. This complicates PGD management, so don't do this. We can keep the PGD mapped and the PUD table all clear - it's only a single 4K page per 512 GB of memory hotplugged. Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Andy Lutomirski <luto@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Waiman Long <Waiman.Long@hp.com> Cc: linux-mm@kvack.org Link: http://lkml.kernel.org/r/064ff6c7275734537f969e876f6cd0baa954d2cc.1468527351.git.luto@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
@@ -702,27 +702,6 @@ static void __meminit free_pmd_table(pmd_t *pmd_start, pud_t *pud)
 	spin_unlock(&init_mm.page_table_lock);
 }
 
-/* Return true if pgd is changed, otherwise return false. */
-static bool __meminit free_pud_table(pud_t *pud_start, pgd_t *pgd)
-{
-	pud_t *pud;
-	int i;
-
-	for (i = 0; i < PTRS_PER_PUD; i++) {
-		pud = pud_start + i;
-		if (!pud_none(*pud))
-			return false;
-	}
-
-	/* free a pud table */
-	free_pagetable(pgd_page(*pgd), 0);
-	spin_lock(&init_mm.page_table_lock);
-	pgd_clear(pgd);
-	spin_unlock(&init_mm.page_table_lock);
-
-	return true;
-}
-
 static void __meminit
 remove_pte_table(pte_t *pte_start, unsigned long addr, unsigned long end,
 		 bool direct)
@@ -913,7 +892,6 @@ remove_pagetable(unsigned long start, unsigned long end, bool direct)
 	unsigned long addr;
 	pgd_t *pgd;
 	pud_t *pud;
-	bool pgd_changed = false;
 
 	for (addr = start; addr < end; addr = next) {
 		next = pgd_addr_end(addr, end);
@@ -924,13 +902,8 @@ remove_pagetable(unsigned long start, unsigned long end, bool direct)
 
 		pud = (pud_t *)pgd_page_vaddr(*pgd);
 		remove_pud_table(pud, addr, next, direct);
-		if (free_pud_table(pud, pgd))
-			pgd_changed = true;
 	}
 
-	if (pgd_changed)
-		sync_global_pgds(start, end - 1, 1);
-
 	flush_tlb_all();
 }
 
