linux-kernel - [PATCH] powerpc/mm/nohash: do not flush the entire mm when range is a single page

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Date:   Tue, 23 Jan 2018 14:22:50 +0100 (CET)
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Scott Wood <oss@...error.net>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH] powerpc/mm/nohash: do not flush the entire mm when range is a
 single page

Most of the time, flush_tlb_range() is called on single pages.
At the time being, flush_tlb_range() inconditionnaly calls
flush_tlb_mm() which flushes at least the entire PID pages and on
older CPUs like 4xx or 8xx it flushes the entire TLB table.

This patch calls flush_tlb_page() instead of flush_tlb_mm() when
the range is a single page.

Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
---
 arch/powerpc/mm/tlb_nohash.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/tlb_nohash.c b/arch/powerpc/mm/tlb_nohash.c
index bfc4a0869609..15fe5f0c8665 100644
--- a/arch/powerpc/mm/tlb_nohash.c
+++ b/arch/powerpc/mm/tlb_nohash.c
@@ -388,7 +388,10 @@ void flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
 		     unsigned long end)
 
 {
-	flush_tlb_mm(vma->vm_mm);
+	if (end - start == PAGE_SIZE && !(start & ~PAGE_MASK))
+		flush_tlb_page(vma, start);
+	else
+		flush_tlb_mm(vma->vm_mm);
 }
 EXPORT_SYMBOL(flush_tlb_range);
 
-- 
2.13.3