Re: [PATCH RFC PKS/PMEM 33/58] fs/cramfs: Utilize new kmap_thread()

[Ira Weiny <ira.weiny@xxxxxxxxx>]

On Tue, Oct 13, 2020 at 08:36:43PM +0100, Matthew Wilcox wrote:
> On Tue, Oct 13, 2020 at 11:44:29AM -0700, Dan Williams wrote:
> > On Fri, Oct 9, 2020 at 12:52 PM <ira.weiny@xxxxxxxxx> wrote:
> > >
> > > From: Ira Weiny <ira.weiny@xxxxxxxxx>
> > >
> > > 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@xxxxxxxxxxx>
> > > Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> > > ---
> > >  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 ?

Christoph had the same idea.  I'll work on it.

Ira