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Subject[PATCH v4 1/1] mm/highmem: Remove deprecated kmap_atomic
Date
From: Ira Weiny <ira.weiny@intel.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@intel.com>
Signed-off-by: Prathu Baronia <prathu.baronia@oneplus.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
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