On Tue, Oct 13, 2020 at 12:37 PM Matthew Wilcox [off-list ref] wrote:

On Tue, Oct 13, 2020 at 11:44:29AM -0700, Dan Williams wrote:

quoted

On Fri, Oct 9, 2020 at 12:52 PM [off-list ref] wrote:

quoted

From: Ira Weiny <ira.weiny@intel.com>

The kmap() calls in this FS are localized to a single thread.  To avoid
the over head of global PKRS updates use the new kmap_thread() call.

Cc: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
---
 fs/cramfs/inode.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c
index 912308600d39..003c014a42ed 100644
--- a/fs/cramfs/inode.c
+++ b/fs/cramfs/inode.c

@@ -247,8 +247,8 @@ static void *cramfs_blkdev_read(struct super_block *sb, unsigned int offset,
                struct page *page = pages[i];

                if (page) {
-                       memcpy(data, kmap(page), PAGE_SIZE);
-                       kunmap(page);
+                       memcpy(data, kmap_thread(page), PAGE_SIZE);
+                       kunmap_thread(page);

Why does this need a sleepable kmap? This looks like a textbook
kmap_atomic() use case.

There's a lot of code of this form.  Could we perhaps have:

static inline void copy_to_highpage(struct page *to, void *vfrom, unsigned int size)
{
        char *vto = kmap_atomic(to);

        memcpy(vto, vfrom, size);
        kunmap_atomic(vto);
}

in linux/highmem.h ?

Nice, yes, that could also replace the local ones in lib/iov_iter.c
(memcpy_{to,from}_page())