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Date: Sat, 10 Oct 2020 01:39:54 +0100
From: Matthew Wilcox <willy@infradead.org>
To: Eric Biggers <ebiggers@kernel.org>
Subject: Re: [PATCH RFC PKS/PMEM 22/58] fs/f2fs: Utilize new kmap_thread()
Message-ID: <20201010003954.GW20115@casper.infradead.org>
References: <20201009195033.3208459-1-ira.weiny@intel.com>
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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@intel.com 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@linutronix.de/