linux-kernel - Re: [RFC Patch v2 2/4] mm/mempolicy: unify the preprocessing for mbind and set

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Date:   Mon, 24 May 2021 13:59:39 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     David Rientjes <rientjes@...gle.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Dave Hansen <dave.hansen@...el.com>,
        Ben Widawsky <ben.widawsky@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>, ying.huang@...el.com
Subject: Re: [RFC Patch v2 2/4] mm/mempolicy: unify the preprocessing for
 mbind and set_mempolicy

On Sun, May 23, 2021 at 10:16:11PM -0700, David Rientjes wrote:
> On Thu, 20 May 2021, Feng Tang wrote:
> 
> > Currently the kernel_mbind() and kernel_set_mempolicy() do almost
> > the same operation for parameter sanity check and preprocessing.
> > 
> > Add a macro to unify the code to reduce the redundancy, and make
> > it easier for changing the pre-processing code in future.
> > 
> > Signed-off-by: Feng Tang <feng.tang@...el.com>
> > ---
> >  mm/mempolicy.c | 46 +++++++++++++++++++---------------------------
> >  1 file changed, 19 insertions(+), 27 deletions(-)
> > 
> > diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> > index 1964cca..0f5bf60 100644
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -1460,25 +1460,29 @@ static int copy_nodes_to_user(unsigned long __user *mask, unsigned long maxnode,
> >  	return copy_to_user(mask, nodes_addr(*nodes), copy) ? -EFAULT : 0;
> >  }
> >  
> > +#define MPOL_PRE_PROCESS() \
> 
> This should be extracted to helper function returning bool, not a macro.

Yes, initially I did try it with an inline function, but as a function
it has quite several input parameters and several output parameters, 
which made the code still big and ugly.

But if community think it's the right direction to go, I can change it.

Thanks,
Feng

> > +	 \
> > +	nodemask_t nodes; \
> > +	int err; \
> > +	unsigned short mode_flags; \
> > +	mode_flags = mode & MPOL_MODE_FLAGS; \
> > +	mode &= ~MPOL_MODE_FLAGS; \
> > +	if (mode >= MPOL_MAX) \
> > +		return -EINVAL; \
> > +	if ((mode_flags & MPOL_F_STATIC_NODES) && \
> > +		(mode_flags & MPOL_F_RELATIVE_NODES)) \
> > +		return -EINVAL; \
> > +	err = get_nodes(&nodes, nmask, maxnode); \
> > +	if (err) \
> > +		return err;
> > +
> >  static long kernel_mbind(unsigned long start, unsigned long len,
> >  			 unsigned long mode, const unsigned long __user *nmask,
> >  			 unsigned long maxnode, unsigned int flags)
> >  {
> > -	nodemask_t nodes;
> > -	int err;
> > -	unsigned short mode_flags;
> > +	MPOL_PRE_PROCESS();
> >  
> >  	start = untagged_addr(start);
> > -	mode_flags = mode & MPOL_MODE_FLAGS;
> > -	mode &= ~MPOL_MODE_FLAGS;
> > -	if (mode >= MPOL_MAX)
> > -		return -EINVAL;
> > -	if ((mode_flags & MPOL_F_STATIC_NODES) &&
> > -	    (mode_flags & MPOL_F_RELATIVE_NODES))
> > -		return -EINVAL;
> > -	err = get_nodes(&nodes, nmask, maxnode);
> > -	if (err)
> > -		return err;
> >  	return do_mbind(start, len, mode, mode_flags, &nodes, flags);
> >  }
> >  
> > @@ -1493,20 +1497,8 @@ SYSCALL_DEFINE6(mbind, unsigned long, start, unsigned long, len,
> >  static long kernel_set_mempolicy(int mode, const unsigned long __user *nmask,
> >  				 unsigned long maxnode)
> >  {
> > -	int err;
> > -	nodemask_t nodes;
> > -	unsigned short flags;
> > -
> > -	flags = mode & MPOL_MODE_FLAGS;
> > -	mode &= ~MPOL_MODE_FLAGS;
> > -	if ((unsigned int)mode >= MPOL_MAX)
> > -		return -EINVAL;
> > -	if ((flags & MPOL_F_STATIC_NODES) && (flags & MPOL_F_RELATIVE_NODES))
> > -		return -EINVAL;
> > -	err = get_nodes(&nodes, nmask, maxnode);
> > -	if (err)
> > -		return err;
> > -	return do_set_mempolicy(mode, flags, &nodes);
> > +	MPOL_PRE_PROCESS();
> > +	return do_set_mempolicy(mode, mode_flags, &nodes);
> >  }
> >  
> >  SYSCALL_DEFINE3(set_mempolicy, int, mode, const unsigned long __user *, nmask,
> > -- 
> > 2.7.4
> > 
> >