[PATCH] kmem_cache_zalloc()

[PATCH] kmem_cache_zalloc()

[Eric Sandeen]

Welcome back Linus -

There was a brief thread on this patch while you were gone, please see 
http://www.uwsg.iu.edu/hypermail/linux/kernel/0203.3/0601.html

In short, we're using a kmem_cache_zalloc() function in XFS which just
does kmem_cache_alloc + memset.

We'd like to incorporate this into the kernel proper, and several others
chimed in that it would be useful, so here's the patch.  If it's a no-go
with you, we can roll this functionality back under fs/xfs to reduce our
changes in the mainline kernel.

Thanks,

-Eric

--- linux-orig/include/linux/slab.h	Mon Mar 18 14:37:14 2002
+++ linux/include/linux/slab.h	Wed Apr  3 14:58:40 2002
@@ -56,6 +56,7 @@
 extern int kmem_cache_destroy(kmem_cache_t *);
 extern int kmem_cache_shrink(kmem_cache_t *);
 extern void *kmem_cache_alloc(kmem_cache_t *, int);
+extern void *kmem_cache_zalloc(kmem_cache_t *, int);
 extern void kmem_cache_free(kmem_cache_t *, void *);
 
 extern void *kmalloc(size_t, int);
--- linux-orig/mm/slab.c	Mon Mar 18 14:37:18 2002
+++ linux/mm/slab.c	Tue Apr  2 12:56:38 2002
@@ -1611,6 +1611,23 @@
 	local_irq_restore(flags);
 }
 
+void *
+kmem_cache_zalloc(kmem_cache_t *cachep, int flags)
+{
+	void    *ptr;
+	ptr = __kmem_cache_alloc(cachep, flags);
+	if (ptr)
+#if DEBUG
+		memset(ptr, 0, cachep->objsize -
+			(cachep->flags & SLAB_RED_ZONE ? 2*BYTES_PER_WORD : 0));
+#else
+		memset(ptr, 0, cachep->objsize);
+#endif
+
+	return ptr;
+}
+
+
 /**
  * kfree - free previously allocated memory
  * @objp: pointer returned by kmalloc.
--- linux-orig/kernel/ksyms.c	Mon Mar 18 14:37:03 2002
+++ linux/kernel/ksyms.c	Tue Apr  2 12:56:38 2002
@@ -102,6 +115,7 @@
 EXPORT_SYMBOL(kmem_cache_destroy);
 EXPORT_SYMBOL(kmem_cache_shrink);
 EXPORT_SYMBOL(kmem_cache_alloc);
+EXPORT_SYMBOL(kmem_cache_zalloc);
 EXPORT_SYMBOL(kmem_cache_free);
 EXPORT_SYMBOL(kmalloc);
 EXPORT_SYMBOL(kfree);


-- 
Eric Sandeen      XFS for Linux     http://oss.sgi.com/projects/xfs
sandeen@sgi.com   SGI, Inc.

Re: [PATCH] kmem_cache_zalloc()

[Tommy Reynolds]

Uttered "Eric Sandeen" <sandeen@sgi.com>, spoke thus:

>  In short, we're using a kmem_cache_zalloc() function in XFS which just
>  does kmem_cache_alloc + memset.
> 
>  We'd like to incorporate this into the kernel proper, and several others
>  chimed in that it would be useful, so here's the patch.  If it's a no-go
>  with you, we can roll this functionality back under fs/xfs to reduce our
>  changes in the mainline kernel.

Why not use the constructor function interface to kmem_cache_create that is
_already_ in the kernel API?

Re: [PATCH] kmem_cache_zalloc()

[Brian Gerst]

Tommy Reynolds wrote:
> 
> Uttered "Eric Sandeen" <sandeen@sgi.com>, spoke thus:
> 
> >  In short, we're using a kmem_cache_zalloc() function in XFS which just
> >  does kmem_cache_alloc + memset.
> >
> >  We'd like to incorporate this into the kernel proper, and several others
> >  chimed in that it would be useful, so here's the patch.  If it's a no-go
> >  with you, we can roll this functionality back under fs/xfs to reduce our
> >  changes in the mainline kernel.
> 
> Why not use the constructor function interface to kmem_cache_create that is
> _already_ in the kernel API?

Constructors are only called once when the slab is allocated.  It is
expected that objects are returned to the slab in the same state.

I think a better idea would be to add a flag to the cache that tells
kmem_cache_alloc() to zero out the object it allocates instead of
creating another interface.

--

				Brian Gerst