linux-kernel - Re: SL*B: drop kmem cache argument from constructor

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Date:	Fri, 11 Jul 2008 12:22:28 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jon Tollefson <kniht@...ux.vnet.ibm.com>
Cc:	Alexey Dobriyan <adobriyan@...il.com>, penberg@...helsinki.fi,
	mpm@...enic.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	cl@...ux-foundation.org, Nick Piggin <nickpiggin@...oo.com.au>
Subject: Re: SL*B: drop kmem cache argument from constructor

On Thu, 10 Jul 2008 11:44:16 -0500 Jon Tollefson <kniht@...ux.vnet.ibm.com> wrote:

> Alexey Dobriyan wrote:
> > Kmem cache passed to constructor is only needed for constructors that are
> > themselves multiplexeres. Nobody uses this "feature", nor does anybody uses
> > passed kmem cache in non-trivial way, so pass only pointer to object.
> >
> > Non-trivial places are:
> > 	arch/powerpc/mm/init_64.c
> > 	arch/powerpc/mm/hugetlbpage.c
> >   
> ...<snip>...
> > --- a/arch/powerpc/mm/hugetlbpage.c
> > +++ b/arch/powerpc/mm/hugetlbpage.c
> > @@ -595,9 +595,9 @@ static int __init hugepage_setup_sz(char *str)
> >  }
> >  __setup("hugepagesz=", hugepage_setup_sz);
> >
> > -static void zero_ctor(struct kmem_cache *cache, void *addr)
> > +static void zero_ctor(void *addr)
> >  {
> > -	memset(addr, 0, kmem_cache_size(cache));
> > +	memset(addr, 0, HUGEPTE_TABLE_SIZE);
> >   
> This isn't going to work with the multiple huge page size support.  The
> HUGEPTE_TABLE_SIZE macro now takes a parameter with of the mmu psize
> index to indicate the size of page.
> 

hrm.  I suppose we could hold our noses and use ksize(), assuming that
we're ready to use ksize() at this stage in the object's lifetime.

Better would be to just use kmem_cache_zalloc()?

--- a/arch/powerpc/mm/hugetlbpage.c~slb-drop-kmem-cache-argument-from-constructor-fix
+++ a/arch/powerpc/mm/hugetlbpage.c
@@ -113,7 +113,7 @@ static inline pte_t *hugepte_offset(huge
 static int __hugepte_alloc(struct mm_struct *mm, hugepd_t *hpdp,
 			   unsigned long address, unsigned int psize)
 {
-	pte_t *new = kmem_cache_alloc(huge_pgtable_cache(psize),
+	pte_t *new = kmem_cache_zalloc(huge_pgtable_cache(psize),
 				      GFP_KERNEL|__GFP_REPEAT);
 
 	if (! new)
@@ -730,11 +730,6 @@ static int __init hugepage_setup_sz(char
 }
 __setup("hugepagesz=", hugepage_setup_sz);
 
-static void zero_ctor(void *addr)
-{
-	memset(addr, 0, HUGEPTE_TABLE_SIZE);
-}
-
 static int __init hugetlbpage_init(void)
 {
 	unsigned int psize;
@@ -756,7 +751,7 @@ static int __init hugetlbpage_init(void)
 						HUGEPTE_TABLE_SIZE(psize),
 						HUGEPTE_TABLE_SIZE(psize),
 						0,
-						zero_ctor);
+						NULL);
 			if (!huge_pgtable_cache(psize))
 				panic("hugetlbpage_init(): could not create %s"\
 				      "\n", HUGEPTE_CACHE_NAME(psize));
_


btw, Nick, what's with that dopey

	huge_pgtable_cache(psize) = kmem_cache_create(...

trick?  The result of a function call is not an lvalue, and writing a
macro which pretends to be a function and then using it in some manner
in which a function cannot be used is seven ways silly :(
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