lib: replace kmap() with kmap_local_page()

kmap() has been deprecated in favor of the kmap_local_page() due to high
cost, restricted mapping space, the overhead of a global lock for
synchronization, and making the process sleep in the absence of free
slots.

kmap_local_page() is faster than kmap() and offers thread-local and
CPU-local mappings, take pagefaults in a local kmap region and preserves
preemption by saving the mappings of outgoing tasks and restoring those of
the incoming one during a context switch.

The mappings are kept thread local in the functions “dmirror_do_read”
and “dmirror_do_write” in test_hmm.c

Therefore, replace kmap() with kmap_local_page() and use
mempcy_from/to_page() to avoid open coding kmap_local_page() + memcpy() +
kunmap_local().

Remove the unused variable “tmp”.

Link: https://lkml.kernel.org/r/20230610175712.GA348514@sumitra.com
Signed-off-by: Sumitra Sharma <sumitraartsy@gmail.com>
Suggested-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Reviewed-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Cc: Deepak R Varma <drv@mailo.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/lib/test_hmm.c b/lib/test_hmm.c
index 67e6f83fe0f82ad0f8d73461290b83262493f9dc..717dcb83012733e919000f13e6c035e86ba2abb4 100644 (file)
--- a/lib/test_hmm.c
+++ b/lib/test_hmm.c
@@ -368,16 +368,13 @@ static int dmirror_do_read(struct dmirror *dmirror, unsigned long start,
        for (pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++) {
                void *entry;
                struct page *page;
-               void *tmp;
 
                entry = xa_load(&dmirror->pt, pfn);
                page = xa_untag_pointer(entry);
                if (!page)
                        return -ENOENT;
 
-               tmp = kmap(page);
-               memcpy(ptr, tmp, PAGE_SIZE);
-               kunmap(page);
+               memcpy_from_page(ptr, page, 0, PAGE_SIZE);
 
                ptr += PAGE_SIZE;
                bounce->cpages++;
@@ -437,16 +434,13 @@ static int dmirror_do_write(struct dmirror *dmirror, unsigned long start,
        for (pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++) {
                void *entry;
                struct page *page;
-               void *tmp;
 
                entry = xa_load(&dmirror->pt, pfn);
                page = xa_untag_pointer(entry);
                if (!page || xa_pointer_tag(entry) != DPT_XA_TAG_WRITE)
                        return -ENOENT;
 
-               tmp = kmap(page);
-               memcpy(tmp, ptr, PAGE_SIZE);
-               kunmap(page);
+               memcpy_to_page(page, 0, ptr, PAGE_SIZE);
 
                ptr += PAGE_SIZE;
                bounce->cpages++;