2002-04-03 22:13:39

by Eric Sandeen

Subject: [PATCH] kmem_cache_zalloc()

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
[email protected] SGI, Inc.

2002-04-03 22:29:50

by Tommy Reynolds

Subject: Re: [PATCH] kmem_cache_zalloc()

Uttered "Eric Sandeen" <[email protected]>, 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?

2002-04-03 22:47:30

by Brian Gerst

Subject: Re: [PATCH] kmem_cache_zalloc()

Tommy Reynolds wrote:
>
> Uttered "Eric Sandeen" <[email protected]>, 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