diff mbox series

mm/memory: Replace kmap() with kmap_local_page()

Message ID 20231214081039.1919328-1-fabio.maria.de.francesco@linux.intel.com
State New
Headers
Series mm/memory: Replace kmap() with kmap_local_page() |

Commit Message

Fabio M. De Francesco Dec. 14, 2023, 8:10 a.m. UTC 
  From: "Fabio M. De Francesco" <fabio.maria.de.francesco@intel.com>

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.

Cc: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Fabio M. De Francesco <fabio.maria.de.francesco@linux.intel.com>
---
 mm/memory.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

Comments

Andrew Morton Dec. 14, 2023, 7:47 p.m. UTC | #1 
> From: "Fabio M. De Francesco" <fabio.maria.de.francesco@linux.intel.com>
> ...
> From: "Fabio M. De Francesco" <fabio.maria.de.francesco@intel.com>
> 
> ...
>
> Signed-off-by: Fabio M. De Francesco <fabio.maria.de.francesco@linux.intel.com>

We get a complaint from checkpatch (and possibly from Stephen Rothwell)
that the From: and Signed-off-by: email addresses differ.

I tentatively rewrote your explicit From: to @linux.intel.com, which
may have been unwelcome.  What can we do here?
Fabio M. De Francesco Dec. 15, 2023, 8:40 a.m. UTC | #2 
On Thursday, 14 December 2023 20:47:47 CET Andrew Morton wrote:
> > From: "Fabio M. De Francesco" <fabio.maria.de.francesco@linux.intel.com>
> > ...
> > From: "Fabio M. De Francesco" <fabio.maria.de.francesco@intel.com>
> > 
> > ...
> > 
> > Signed-off-by: Fabio M. De Francesco
> > <fabio.maria.de.francesco@linux.intel.com>
> We get a complaint from checkpatch (and possibly from Stephen Rothwell)
> that the From: and Signed-off-by: email addresses differ.
> 
> I tentatively rewrote your explicit From: to @linux.intel.com, which
> may have been unwelcome.  What can we do here?

I have two email addresses and sometimes some confusion arises while 
configuring. Please discard this patch. I'm going to send another to replace 
this.

Thanks,

Fabio
Fabio M. De Francesco Dec. 15, 2023, 4:17 p.m. UTC | #3 
On Friday, 15 December 2023 09:40:33 CET Fabio M. De Francesco wrote:
> On Thursday, 14 December 2023 20:47:47 CET Andrew Morton wrote:
> >
> > [skip]
> >
> > I tentatively rewrote your explicit From: to @linux.intel.com, which
> > may have been unwelcome.  What can we do here?
> 
Sorry, in my last message I asked you to discard this patch and sent another 
one but I hadn't yet understood that you rewrote and accepted it. My English 
is still not good enough. Thanks for rewriting it. I'm perfectly fine with your 
decision to rewrite it to @linux.intel.com.

Fabio
diff mbox series

Patch

diff --git a/mm/memory.c b/mm/memory.c
index 7d9f6b685032..88377a107fbe 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5852,7 +5852,7 @@  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);
@@ -5861,8 +5861,7 @@  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;