powerpc/mm: Reduce memory usage for mm_context_t for radix

Currently, our mm_context_t on book3s64 include all hash specific
context details like slice mask and subpage protection details. We
can skip allocating these with radix translation. This will help us to save
8K per mm_context with radix translation.

With the patch applied we have

sizeof(mm_context_t)  = 136
sizeof(struct hash_mm_context)  = 8288

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 15 insertions, 1 deletions

diff --git a/arch/powerpc/mm/mmu_context_book3s64.c b/arch/powerpc/mm/mmu_context_book3s64.c
index f720c5cc0b5e..6eef5a36b2e9 100644
--- a/arch/powerpc/mm/mmu_context_book3s64.c
+++ b/arch/powerpc/mm/mmu_context_book3s64.c
@@ -63,6 +63,12 @@ static int hash__init_new_context(struct mm_struct *mm)
 	if (index < 0)
 		return index;
 
+	mm->context.hash_context = kmalloc(sizeof(struct hash_mm_context), GFP_KERNEL);
+	if (!mm->context.hash_context) {
+		ida_free(&mmu_context_ida, index);
+		return -ENOMEM;
+	}
+
 	/*
 	 * The old code would re-promote on fork, we don't do that when using
 	 * slices as it could cause problem promoting slices that have been
@@ -77,8 +83,14 @@ static int hash__init_new_context(struct mm_struct *mm)
 	 * We should not be calling init_new_context() on init_mm. Hence a
 	 * check against 0 is OK.
 	 */
-	if (mm->context.id == 0)
+	if (mm->context.id == 0) {
+		memset(mm->context.hash_context, 0, sizeof(struct hash_mm_context));
 		slice_init_new_context_exec(mm);
+	} else {
+		/* This is fork. Copy hash_context details from current->mm */
+		memcpy(mm->context.hash_context, current->mm->context.hash_context, sizeof(struct hash_mm_context));
+
+	}
 
 	subpage_prot_init_new_context(mm);
 
@@ -118,6 +130,7 @@ static int radix__init_new_context(struct mm_struct *mm)
 	asm volatile("ptesync;isync" : : : "memory");
 
 	mm->context.npu_context = NULL;
+	mm->context.hash_context = NULL;
 
 	return index;
 }
@@ -162,6 +175,7 @@ static void destroy_contexts(mm_context_t *ctx)
 		if (context_id)
 			ida_free(&mmu_context_ida, context_id);
 	}
+	kfree(ctx->hash_context);
 }
 
 static void pmd_frag_destroy(void *pmd_frag)