The patch titled
Subject: checkpatch: Add kmap and kmap_atomic to the deprecated list
has been added to the -mm mm-nonmm-unstable branch. Its filename is
checkpatch-add-kmap-and-kmap_atomic-to-the-deprecated-list.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/checkpatch-add-kmap-and-kmap_atomic-to-the-deprecated-list.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Ira Weiny <ira.weiny@xxxxxxxxx>
Subject: checkpatch: Add kmap and kmap_atomic to the deprecated list
Date: Sat, 13 Aug 2022 15:00:34 -0700
kmap() and kmap_atomic() are being deprecated in favor of
kmap_local_page().
There are two main problems with kmap(): (1) It comes with an overhead as
mapping space is restricted and protected by a global lock for
synchronization and (2) it also requires global TLB invalidation when the
kmap's pool wraps and it might block when the mapping space is fully
utilized until a slot becomes available.
kmap_local_page() is safe from any context and is therefore redundant with
kmap_atomic() with the exception of any pagefault or preemption disable
requirements. However, using kmap_atomic() for these side effects makes
the code less clear. So any requirement for pagefault or preemption
disable should be made explicitly.
With kmap_local_page() the mappings are per thread, CPU local, can take
page faults, and can be called from any context (including interrupts).
It is faster than kmap() in kernels with HIGHMEM enabled. Furthermore,
the tasks can be preempted and, when they are scheduled to run again, the
kernel virtual addresses are restored.
Link: https://lkml.kernel.org/r/20220813220034.806698-1-ira.weiny@xxxxxxxxx
Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Suggested-by: Fabio M. De Francesco <fmdefrancesco@xxxxxxxxx>
Cc: Joe Perches <joe@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
scripts/checkpatch.pl | 2 ++
1 file changed, 2 insertions(+)
--- a/scripts/checkpatch.pl~checkpatch-add-kmap-and-kmap_atomic-to-the-deprecated-list
+++ a/scripts/checkpatch.pl
@@ -807,6 +807,8 @@ our %deprecated_apis = (
"rcu_barrier_sched" => "rcu_barrier",
"get_state_synchronize_sched" => "get_state_synchronize_rcu",
"cond_synchronize_sched" => "cond_synchronize_rcu",
+ "kmap" => "kmap_local_page",
+ "kmap_atomic" => "kmap_local_page",
);
#Create a search pattern for all these strings to speed up a loop below
_
Patches currently in -mm which might be from ira.weiny@xxxxxxxxx are
checkpatch-add-kmap-and-kmap_atomic-to-the-deprecated-list.patch
