linux-kernel - [PATCH v4 1/1] mm/highmem: Remove deprecated kmap

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Date:   Thu,  4 Feb 2021 13:02:53 +0530
From:   Prathu Baronia <prathubaronia2011@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     chintan.pandya@...plus.com, Ira Weiny <ira.weiny@...el.com>,
        Prathu Baronia <prathu.baronia@...plus.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: [PATCH v4 1/1] mm/highmem: Remove deprecated kmap_atomic

From: Ira Weiny <ira.weiny@...el.com>

kmap_atomic() is being deprecated in favor of kmap_local_page().

Replace the uses of kmap_atomic() within the highmem code.

On profiling clear_huge_page() using ftrace an improvement
of 62% was observed on the below setup.

Setup:-
Below data has been collected on Qualcomm's SM7250 SoC THP enabled
(kernel v4.19.113) with only CPU-0(Cortex-A55) and CPU-7(Cortex-A76)
switched on and set to max frequency, also DDR set to perf governor.

FTRACE Data:-

Base data:-
Number of iterations: 48
Mean of allocation time: 349.5 us
std deviation: 74.5 us

v4 data:-
Number of iterations: 48
Mean of allocation time: 131 us
std deviation: 32.7 us

The following simple userspace experiment to allocate
100MB(BUF_SZ) of pages and writing to it gave us a good insight,
we observed an improvement of 42% in allocation and writing timings.
-------------------------------------------------------------
Test code snippet
-------------------------------------------------------------
      clock_start();
      buf = malloc(BUF_SZ); /* Allocate 100 MB of memory */

        for(i=0; i < BUF_SZ_PAGES; i++)
        {
                *((int *)(buf + (i*PAGE_SIZE))) = 1;
        }
      clock_end();
-------------------------------------------------------------

Malloc test timings for 100MB anon allocation:-

Base data:-
Number of iterations: 100
Mean of allocation time: 31831 us
std deviation: 4286 us

v4 data:-
Number of iterations: 100
Mean of allocation time: 18193 us
std deviation: 4915 us

Signed-off-by: Ira Weiny <ira.weiny@...el.com>
Signed-off-by: Prathu Baronia <prathu.baronia@...plus.com>
[Updated commit text with test data]
---
 include/linux/highmem.h | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index d2c70d3772a3..9a202c7e4e26 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -146,9 +146,9 @@ static inline void invalidate_kernel_vmap_range(void *vaddr, int size)
 #ifndef clear_user_highpage
 static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
 {
-	void *addr = kmap_atomic(page);
+	void *addr = kmap_local_page(page);
 	clear_user_page(addr, vaddr, page);
-	kunmap_atomic(addr);
+	kunmap_local(addr);
 }
 #endif
 
@@ -199,9 +199,9 @@ alloc_zeroed_user_highpage_movable(struct vm_area_struct *vma,
 
 static inline void clear_highpage(struct page *page)
 {
-	void *kaddr = kmap_atomic(page);
+	void *kaddr = kmap_local_page(page);
 	clear_page(kaddr);
-	kunmap_atomic(kaddr);
+	kunmap_local(kaddr);
 }
 
 /*
@@ -216,7 +216,7 @@ static inline void zero_user_segments(struct page *page,
 		unsigned start1, unsigned end1,
 		unsigned start2, unsigned end2)
 {
-	void *kaddr = kmap_atomic(page);
+	void *kaddr = kmap_local_page(page);
 	unsigned int i;
 
 	BUG_ON(end1 > page_size(page) || end2 > page_size(page));
@@ -227,7 +227,7 @@ static inline void zero_user_segments(struct page *page,
 	if (end2 > start2)
 		memset(kaddr + start2, 0, end2 - start2);
 
-	kunmap_atomic(kaddr);
+	kunmap_local(kaddr);
 	for (i = 0; i < compound_nr(page); i++)
 		flush_dcache_page(page + i);
 }
@@ -252,11 +252,11 @@ static inline void copy_user_highpage(struct page *to, struct page *from,
 {
 	char *vfrom, *vto;
 
-	vfrom = kmap_atomic(from);
-	vto = kmap_atomic(to);
+	vfrom = kmap_local_page(from);
+	vto = kmap_local_page(to);
 	copy_user_page(vto, vfrom, vaddr, to);
-	kunmap_atomic(vto);
-	kunmap_atomic(vfrom);
+	kunmap_local(vto);
+	kunmap_local(vfrom);
 }
 
 #endif
@@ -267,11 +267,11 @@ static inline void copy_highpage(struct page *to, struct page *from)
 {
 	char *vfrom, *vto;
 
-	vfrom = kmap_atomic(from);
-	vto = kmap_atomic(to);
+	vfrom = kmap_local_page(from);
+	vto = kmap_local_page(to);
 	copy_page(vto, vfrom);
-	kunmap_atomic(vto);
-	kunmap_atomic(vfrom);
+	kunmap_local(vto);
+	kunmap_local(vfrom);
 }
 
 #endif
-- 
2.17.1