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authorFabio M. De Francesco <fabio.maria.de.francesco@linux.intel.com>2023-12-14 11:10:04 +0300
committerAndrew Morton <akpm@linux-foundation.org>2023-12-21 01:48:14 +0300
commitf7ef5fe74aaf634f2fe50e0f3339a405cced5d01 (patch)
tree45c8e35188a6012904f179768dae2d06975a43be /mm/memory.c
parent0abfa8efad8dccc3899f64dafa985a251714a709 (diff)
downloadlinux-f7ef5fe74aaf634f2fe50e0f3339a405cced5d01.tar.xz
mm/memory: replace kmap() with kmap_local_page()
kmap() has been deprecated in favor of kmap_local_page(). Therefore, replace kmap() with kmap_local_page() in mm/memory.c. There are two main problems with kmap(): (1) It comes with an overhead as the 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. 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. The tasks can be preempted and, when they are scheduled to run again, the kernel virtual addresses are restored and still valid. Obviously, thread locality implies that the kernel virtual addresses returned by kmap_local_page() are only valid in the context of the callers (i.e., they cannot be handed to other threads). The use of kmap_local_page() in mm/memory.c does not break the above-mentioned assumption, so it is allowed and preferred. Link: https://lkml.kernel.org/r/20231215084417.2002370-1-fabio.maria.de.francesco@linux.intel.com Link: https://lkml.kernel.org/r/20231214081039.1919328-1-fabio.maria.de.francesco@linux.intel.com Signed-off-by: Fabio M. De Francesco <fabio.maria.de.francesco@linux.intel.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/memory.c')
-rw-r--r--mm/memory.c5
1 files changed, 2 insertions, 3 deletions
diff --git a/mm/memory.c b/mm/memory.c
index 3c530b639559..b9cc56a75f4b 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5944,7 +5944,7 @@ static int __access_remote_vm(struct mm_struct *mm, unsigned long addr,
if (bytes > PAGE_SIZE-offset)
bytes = PAGE_SIZE-offset;
- maddr = kmap(page);
+ maddr = kmap_local_page(page);
if (write) {
copy_to_user_page(vma, page, addr,
maddr + offset, buf, bytes);
@@ -5953,8 +5953,7 @@ static int __access_remote_vm(struct mm_struct *mm, unsigned long addr,
copy_from_user_page(vma, page, addr,
buf, maddr + offset, bytes);
}
- kunmap(page);
- put_page(page);
+ unmap_and_put_page(page, maddr);
}
len -= bytes;
buf += bytes;