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Date: Tue, 13 Oct 2020 13:45:37 -0700
From: Ira Weiny <ira.weiny@intel.com>
To: Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH RFC PKS/PMEM 33/58] fs/cramfs: Utilize new kmap_thread()
Message-ID: <20201013204537.GH2046448@iweiny-DESK2.sc.intel.com>
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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@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 ?

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

Ira