mm/zswap: 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
zswap.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/zswap.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/20231127160058.586446-1-fabio.maria.de.francesco@linux.intel.com
Signed-off-by: Fabio M. De Francesco <fabio.maria.de.francesco@linux.intel.com>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
Acked-by: Chris Li <chrisl@kernel.org> (Google)
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Dan Streetman <ddstreet@ieee.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/zswap.c b/mm/zswap.c
index 74411dfdad92575b8c63a0454d8e5a4453e3368c..699c6ee112222b2e9aef822d697d3e4dbb70a079 100644 (file)
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1267,16 +1267,16 @@ bool zswap_store(struct folio *folio)
        }
 
        if (zswap_same_filled_pages_enabled) {
-               src = kmap_atomic(page);
+               src = kmap_local_page(page);
                if (zswap_is_page_same_filled(src, &value)) {
-                       kunmap_atomic(src);
+                       kunmap_local(src);
                        entry->swpentry = swp_entry(type, offset);
                        entry->length = 0;
                        entry->value = value;
                        atomic_inc(&zswap_same_filled_pages);
                        goto insert_entry;
                }
-               kunmap_atomic(src);
+               kunmap_local(src);
        }
 
        if (!zswap_non_same_filled_pages_enabled)
@@ -1422,9 +1422,9 @@ bool zswap_load(struct folio *folio)
        spin_unlock(&tree->lock);
 
        if (!entry->length) {
-               dst = kmap_atomic(page);
+               dst = kmap_local_page(page);
                zswap_fill_page(dst, entry->value);
-               kunmap_atomic(dst);
+               kunmap_local(dst);
                ret = true;
                goto stats;
        }