Commit 829c3151 authored by Fabio M. De Francesco's avatar Fabio M. De Francesco Committed by Andrew Morton
Browse files

mm/swapfile: replace kmap_atomic() with kmap_local_page() 

kmap_atomic() has been deprecated in favor of kmap_local_page().

Therefore, replace kmap_atomic() with kmap_local_page() in swapfile.c.

kmap_atomic() is implemented like a kmap_local_page() which also disables
page-faults and preemption (the latter only in !PREEMPT_RT kernels).  The
kernel virtual addresses returned by these two API are only valid in the
context of the callers (i.e., they cannot be handed to other threads).

With kmap_local_page() the mappings are per thread and CPU local like in
kmap_atomic(); however, they can handle page-faults and can be called from
any context (including interrupts).  The tasks that call kmap_local_page()
can be preempted and, when they are scheduled to run again, the kernel
virtual addresses are restored and are still valid.

In mm/swapfile.c, the blocks of code between the mappings and un-mappings
do not depend on the above-mentioned side effects of kmap_atomic(), so
that the mere replacements of the old API with the new one is all that is
required (i.e., there is no need to explicitly call pagefault_disable()
and/or preempt_disable()).

Link: https://lkml.kernel.org/r/20231127155452.586387-1-fabio.maria.de.francesco@linux.intel.com


Signed-off-by: default avatarFabio M. De Francesco <fabio.maria.de.francesco@linux.intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 003ae2fb

mm/swapfile.c

+17 −17
Original line number Diff line number Diff line
@@ -1495,9 +1495,9 @@ int swp_swapcount(swp_entry_t entry) 


	do {

		page = list_next_entry(page, lru);

		map = kmap_atomic(page);

		map = kmap_local_page(page);

		tmp_count = map[offset];

		kunmap_atomic(map);

		kunmap_local(map);



		count += (tmp_count & ~COUNT_CONTINUED) * n;

		n *= (SWAP_CONT_MAX + 1);
@@ -3477,9 +3477,9 @@ int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask) 
		if (!(count & COUNT_CONTINUED))

			goto out_unlock_cont;



		map = kmap_atomic(list_page) + offset;

		map = kmap_local_page(list_page) + offset;

		count = *map;

		kunmap_atomic(map);

		kunmap_local(map);



		/*

		 * If this continuation count now has some space in it,
@@ -3529,7 +3529,7 @@ static bool swap_count_continued(struct swap_info_struct *si, 
	spin_lock(&si->cont_lock);

	offset &= ~PAGE_MASK;

	page = list_next_entry(head, lru);

	map = kmap_atomic(page) + offset;

	map = kmap_local_page(page) + offset;



	if (count == SWAP_MAP_MAX)	/* initial increment from swap_map */

		goto init_map;		/* jump over SWAP_CONT_MAX checks */
@@ -3539,27 +3539,27 @@ static bool swap_count_continued(struct swap_info_struct *si, 
		 * Think of how you add 1 to 999

		 */

		while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {

			kunmap_atomic(map);

			kunmap_local(map);

			page = list_next_entry(page, lru);

			BUG_ON(page == head);

			map = kmap_atomic(page) + offset;

			map = kmap_local_page(page) + offset;

		}

		if (*map == SWAP_CONT_MAX) {

			kunmap_atomic(map);

			kunmap_local(map);

			page = list_next_entry(page, lru);

			if (page == head) {

				ret = false;	/* add count continuation */

				goto out;

			}

			map = kmap_atomic(page) + offset;

			map = kmap_local_page(page) + offset;

init_map:		*map = 0;		/* we didn't zero the page */

		}

		*map += 1;

		kunmap_atomic(map);

		kunmap_local(map);

		while ((page = list_prev_entry(page, lru)) != head) {

			map = kmap_atomic(page) + offset;

			map = kmap_local_page(page) + offset;

			*map = COUNT_CONTINUED;

			kunmap_atomic(map);

			kunmap_local(map);

		}

		ret = true;			/* incremented */
@@ -3569,21 +3569,21 @@ init_map: *map = 0; /* we didn't zero the page */ 
		 */

		BUG_ON(count != COUNT_CONTINUED);

		while (*map == COUNT_CONTINUED) {

			kunmap_atomic(map);

			kunmap_local(map);

			page = list_next_entry(page, lru);

			BUG_ON(page == head);

			map = kmap_atomic(page) + offset;

			map = kmap_local_page(page) + offset;

		}

		BUG_ON(*map == 0);

		*map -= 1;

		if (*map == 0)

			count = 0;

		kunmap_atomic(map);

		kunmap_local(map);

		while ((page = list_prev_entry(page, lru)) != head) {

			map = kmap_atomic(page) + offset;

			map = kmap_local_page(page) + offset;

			*map = SWAP_CONT_MAX | count;

			count = COUNT_CONTINUED;

			kunmap_atomic(map);

			kunmap_local(map);

		}

		ret = count == COUNT_CONTINUED;

	}