linux-kernel - [RFC PATCH 2/2] mm/mmu_gather: Avoid multiple page walk cache flush

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Date:   Tue, 17 Dec 2019 12:46:01 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     akpm@...ux-foundation.org, npiggin@...il.com, mpe@...erman.id.au
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Subject: [RFC PATCH 2/2] mm/mmu_gather: Avoid multiple page walk cache flush

On tlb_finish_mmu() kernel does a tlb flush before  mmu gather table invalidate.
The mmu gather table invalidate depending on kernel config also does another
TLBI. Avoid the later on tlb_finish_mmu().

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
---
 mm/mmu_gather.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
index 7c1b8f67af7b..7e2bd43b9084 100644
--- a/mm/mmu_gather.c
+++ b/mm/mmu_gather.c
@@ -143,17 +143,23 @@ static void tlb_remove_table_rcu(struct rcu_head *head)
 	free_page((unsigned long)batch);
 }
 
-static void tlb_table_flush(struct mmu_gather *tlb)
+static void __tlb_table_flush(struct mmu_gather *tlb, bool table_inval)
 {
 	struct mmu_table_batch **batch = &tlb->batch;
 
 	if (*batch) {
-		tlb_table_invalidate(tlb);
+		if (table_inval)
+			tlb_table_invalidate(tlb);
 		call_rcu(&(*batch)->rcu, tlb_remove_table_rcu);
 		*batch = NULL;
 	}
 }
 
+static void tlb_table_flush(struct mmu_gather *tlb)
+{
+	__tlb_table_flush(tlb, true);
+}
+
 void tlb_remove_table(struct mmu_gather *tlb, void *table)
 {
 	struct mmu_table_batch **batch = &tlb->batch;
@@ -178,7 +184,7 @@ void tlb_remove_table(struct mmu_gather *tlb, void *table)
 static void tlb_flush_mmu_free(struct mmu_gather *tlb)
 {
 #ifdef CONFIG_HAVE_RCU_TABLE_FREE
-	tlb_table_flush(tlb);
+	__tlb_table_flush(tlb, false);
 #endif
 #ifndef CONFIG_HAVE_MMU_GATHER_NO_GATHER
 	tlb_batch_pages_flush(tlb);
-- 
2.23.0