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SubjectRe: [PATCH RFC PKS/PMEM 33/58] fs/cramfs: Utilize new kmap_thread()
On Tue, Oct 13, 2020 at 11:44:29AM -0700, Dan Williams wrote:
> On Fri, Oct 9, 2020 at 12:52 PM <ira.weiny@intel.com> wrote:
> >
> > 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 ?

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