linux-kernel - Re: [PATCH v5 1/7] pmem: add wb_cache

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Date:	Tue, 22 Dec 2015 17:00:10 -0700
From:	Ross Zwisler <ross.zwisler@...ux.intel.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Theodore Ts'o <tytso@....edu>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Dave Chinner <david@...morbit.com>,
	Ingo Molnar <mingo@...hat.com>, Jan Kara <jack@...e.com>,
	Jeff Layton <jlayton@...chiereds.net>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-nvdimm@...1.01.org, x86@...nel.org,
	xfs@....sgi.com, Dan Williams <dan.j.williams@...el.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v5 1/7] pmem: add wb_cache_pmem() to the PMEM API

On Tue, Dec 22, 2015 at 02:44:40PM -0800, Andrew Morton wrote:
> On Fri, 18 Dec 2015 22:22:14 -0700 Ross Zwisler <ross.zwisler@...ux.intel.com> wrote:
> 
> > The function __arch_wb_cache_pmem() was already an internal implementation
> > detail of the x86 PMEM API, but this functionality needs to be exported as
> > part of the general PMEM API to handle the fsync/msync case for DAX mmaps.
> > 
> > One thing worth noting is that we really do want this to be part of the
> > PMEM API as opposed to a stand-alone function like clflush_cache_range()
> > because of ordering restrictions.  By having wb_cache_pmem() as part of the
> > PMEM API we can leave it unordered, call it multiple times to write back
> > large amounts of memory, and then order the multiple calls with a single
> > wmb_pmem().
> > 
> > @@ -138,7 +139,7 @@ static inline void arch_clear_pmem(void __pmem *addr, size_t size)
> >  	else
> >  		memset(vaddr, 0, size);
> >  
> > -	__arch_wb_cache_pmem(vaddr, size);
> > +	arch_wb_cache_pmem(addr, size);
> >  }
> >  
> 
> reject.  I made this
> 
> 	arch_wb_cache_pmem(vaddr, size);
> 
> due to Dan's
> http://www.ozlabs.org/~akpm/mmots/broken-out/pmem-dax-clean-up-clear_pmem.patch

The first argument seems wrong to me - in arch_clear_pmem() 'addr' and 'vaddr'
are the same address, with the only difference being 'addr' has the __pmem
annotation.

As of this patch arch_wb_cache_pmem() follows the lead of the rest of the
exported PMEM API functions and takes an argument that has the __pmem
annotation, so I believe it should be:

arch_wb_cache_pmem(addr, size);

Without this I think you'll get a sparse warning.

This will be fixed up in the next version of my series which build upon Dan's
patches.
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