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

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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>
This commit is contained in:
Fabio M. De Francesco 2023-11-27 16:55:21 +01:00 committed by Andrew Morton
parent 27873192ac
commit 003ae2fb0b
1 changed files with 5 additions and 5 deletions
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10
mm/zswap.c
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@ -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;
}