The patch titled
Subject: mm/swapfile: replace kmap_atomic() with kmap_local_page()
has been added to the -mm mm-unstable branch. Its filename is
mm-swapfile-replace-kmap_atomic-with-kmap_local_page.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-swapfile-replace-kmap_atomic-with-kmap_local_page.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: "Fabio M. De Francesco" <fabio.maria.de.francesco@xxxxxxxxxxxxxxx>
Subject: mm/swapfile: replace kmap_atomic() with kmap_local_page()
Date: Mon, 27 Nov 2023 16:54:37 +0100
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@xxxxxxxxxxxxxxx
Signed-off-by: Fabio M. De Francesco <fabio.maria.de.francesco@xxxxxxxxxxxxxxx>
Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/swapfile.c | 34 +++++++++++++++++-----------------
1 file changed, 17 insertions(+), 17 deletions(-)
--- a/mm/swapfile.c~mm-swapfile-replace-kmap_atomic-with-kmap_local_page
+++ a/mm/swapfile.c
@@ -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_entr
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
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
* 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
*/
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;
}
_
Patches currently in -mm which might be from fabio.maria.de.francesco@xxxxxxxxxxxxxxx are
mm-util-use-kmap_local_page-in-memcmp_pages.patch
mm-memory-use-kmap_local_page-in-__wp_page_copy_user.patch
mm-mempool-replace-kmap_atomic-with-kmap_local_page.patch
mm-page_poison-replace-kmap_atomic-with-kmap_local_page.patch
mm-zswap-replace-kmap_atomic-with-kmap_local_page.patch
mm-swapfile-replace-kmap_atomic-with-kmap_local_page.patch
