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.comSigned-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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>