Commit ae96e0cd authored by Sumitra Sharma's avatar Sumitra Sharma Committed by Andrew Morton
Browse files

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: default avatarSumitra Sharma <sumitraartsy@gmail.com>
Suggested-by: default avatarFabio M. De Francesco <fmdefrancesco@gmail.com>
Reviewed-by: default avatarFabio M. De Francesco <fmdefrancesco@gmail.com>
Reviewed-by: default avatarIra Weiny <ira.weiny@intel.com>
Cc: Deepak R Varma <drv@mailo.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent f58a2dd8

lib/test_hmm.c

+2 −8
Original line number Diff line number Diff line
@@ -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++;