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 16:32:43 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     David Rientjes <rientjes@...gle.com>
Cc:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.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>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Widawsky, Ben" <ben.widawsky@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "Huang, Ying" <ying.huang@...el.com>
Subject: Re: [RFC Patch v2 2/4] mm/mempolicy: unify the preprocessing for
 mbind and set_mempolicy

On Mon, May 24, 2021 at 01:59:39PM +0800, Tang, Feng wrote:
> 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.

Following is a patch to unify the preprocssing by using a helper function,
please review, thanks

- Feng

---
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index d79fa299b70c..8e4f47f925b6 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1460,6 +1460,20 @@ static int copy_nodes_to_user(unsigned long __user *mask, unsigned long maxnode,
 	return copy_to_user(mask, nodes_addr(*nodes), copy) ? -EFAULT : 0;
 }
 
+static inline int mpol_pre_process(int *mode, const unsigned long __user *nmask, unsigned long maxnode, nodemask_t *nodes, unsigned short *flags)
+{
+	int ret;
+
+	*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;
+	ret = get_nodes(nodes, nmask, maxnode);
+	return ret;
+}
+
 static long kernel_mbind(unsigned long start, unsigned long len,
 			 unsigned long mode, const unsigned long __user *nmask,
 			 unsigned long maxnode, unsigned int flags)
@@ -1467,19 +1481,14 @@ static long kernel_mbind(unsigned long start, unsigned long len,
 	nodemask_t nodes;
 	int err;
 	unsigned short mode_flags;
+	int lmode = mode;
 
-	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);
+	err = mpol_pre_process(&lmode, nmask, maxnode, &nodes, &mode_flags);
 	if (err)
 		return err;
-	return do_mbind(start, len, mode, mode_flags, &nodes, flags);
+
+	start = untagged_addr(start);
+	return do_mbind(start, len, lmode, mode_flags, &nodes, flags);
 }
 
 SYSCALL_DEFINE6(mbind, unsigned long, start, unsigned long, len,
@@ -1495,18 +1504,14 @@ static long kernel_set_mempolicy(int mode, const unsigned long __user *nmask,
 {
 	int err;
 	nodemask_t nodes;
-	unsigned short flags;
+	unsigned short mode_flags;
+	int lmode = mode;
 
-	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);
+	err = mpol_pre_process(&lmode, nmask, maxnode, &nodes, &mode_flags);
 	if (err)
 		return err;
-	return do_set_mempolicy(mode, flags, &nodes);
+
+	return do_set_mempolicy(lmode, mode_flags, &nodes);
 }
 
 SYSCALL_DEFINE3(set_mempolicy, int, mode, const unsigned long __user *, nmask,