Re: [PATCH RFC PKS/PMEM 22/58] fs/f2fs: Utilize new kmap_thread()

[Matthew Wilcox <willy@xxxxxxxxxxxxx>]

On Fri, Oct 09, 2020 at 02:34:34PM -0700, Eric Biggers wrote:
> On Fri, Oct 09, 2020 at 12:49:57PM -0700, ira.weiny@xxxxxxxxx wrote:
> > 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.
> >
> > @@ -2410,12 +2410,12 @@ static inline struct page *f2fs_pagecache_get_page(
> >  
> >  static inline void f2fs_copy_page(struct page *src, struct page *dst)
> >  {
> > -   char *src_kaddr = kmap(src);
> > -   char *dst_kaddr = kmap(dst);
> > +   char *src_kaddr = kmap_thread(src);
> > +   char *dst_kaddr = kmap_thread(dst);
> >  
> >     memcpy(dst_kaddr, src_kaddr, PAGE_SIZE);
> > -   kunmap(dst);
> > -   kunmap(src);
> > +   kunmap_thread(dst);
> > +   kunmap_thread(src);
> >  }
> 
> Wouldn't it make more sense to switch cases like this to kmap_atomic()?
> The pages are only mapped to do a memcpy(), then they're immediately unmapped.

Maybe you missed the earlier thread from Thomas trying to do something
similar for rather different reasons ...

https://lore.kernel.org/lkml/20200919091751.011116649@xxxxxxxxxxxxx/