[patch 199/262] mm/highmem: remove deprecated kmap_atomic

Andrew Morton
2021-11-05T20:45:19Z

From: Ira Weiny <ira.weiny@intel.com>
Subject: mm/highmem: remove deprecated kmap_atomic

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

[willy@infradead.org: fix zero_user_segments()]
Link: https://lkml.kernel.org/r/YYVhHCJcm2DM2G9u@casper.infradead.org
Link: https://lkml.kernel.org/r/20210204073255.20769-2-prathu.baronia@oneplus.com
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Prathu Baronia <prathu.baronia@oneplus.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

include/linux/highmem.h | 28 ++++++++++++++--------------
mm/highmem.c | 6 +++---
2 files changed, 17 insertions(+), 17 deletions(-)

--- a/include/linux/highmem.h~mm-highmem-remove-deprecated-kmap_atomic
+++ a/include/linux/highmem.h
@@ -143,9 +143,9 @@ static inline void invalidate_kernel_vma
#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

@@ -177,9 +177,9 @@ alloc_zeroed_user_highpage_movable(struc

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);
}

#ifndef __HAVE_ARCH_TAG_CLEAR_HIGHPAGE
@@ -202,7 +202,7 @@ static inline void zero_user_segments(st
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));
@@ -213,7 +213,7 @@ static inline void zero_user_segments(st
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);
}
@@ -238,11 +238,11 @@ static inline void copy_user_highpage(st
{
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
@@ -253,11 +253,11 @@ static inline void copy_highpage(struct
{
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
--- a/mm/highmem.c~mm-highmem-remove-deprecated-kmap_atomic
+++ a/mm/highmem.c
@@ -383,7 +383,7 @@ void zero_user_segments(struct page *pag
unsigned this_end = min_t(unsigned, end1, PAGE_SIZE);

if (end1 > start1) {
- kaddr = kmap_atomic(page + i);
+ kaddr = kmap_local_page(page + i);
memset(kaddr + start1, 0, this_end - start1);
}
end1 -= this_end;
@@ -398,7 +398,7 @@ void zero_user_segments(struct page *pag

if (end2 > start2) {
if (!kaddr)
- kaddr = kmap_atomic(page + i);
+ kaddr = kmap_local_page(page + i);
memset(kaddr + start2, 0, this_end - start2);
}
end2 -= this_end;
@@ -406,7 +406,7 @@ void zero_user_segments(struct page *pag
}

if (kaddr) {
- kunmap_atomic(kaddr);
+ kunmap_local(kaddr);
flush_dcache_page(page + i);
}

_