[PATCH] Do not pass the SLAB flags as GFP in slob kmem_cache_create

[PATCH] Do not pass the SLAB flags as GFP in slob kmem_cache_create

[Catalin Marinas]

It looks like the kmem_cache_create() function in the slob allocator
passes the SLAB flags as GFP flags to the slob_alloc() function. The
patch changes this call to pass GFP_KERNEL as the other allocators seem
to do.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Matt Mackall <mpm@selenic.com>
---
 mm/slob.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/slob.c b/mm/slob.c
index ff5a98d..dce9258 100644
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -538,7 +538,7 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
 	struct kmem_cache *c;
 
 	c = slob_alloc(sizeof(struct kmem_cache),
-		flags, ARCH_KMALLOC_MINALIGN, -1);
+		GFP_KERNEL, ARCH_KMALLOC_MINALIGN, -1);
 
 	if (c) {
 		c->name = name;

Re: [PATCH] Do not pass the SLAB flags as GFP in slob kmem_cache_create

[Cyrill Gorcunov]

[Catalin Marinas - Wed, Dec 10, 2008 at 05:36:33PM +0000]
| It looks like the kmem_cache_create() function in the slob allocator
| passes the SLAB flags as GFP flags to the slob_alloc() function. The
| patch changes this call to pass GFP_KERNEL as the other allocators seem
| to do.
| 
| Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
| Cc: Matt Mackall <mpm@selenic.com>
| ---
|  mm/slob.c |    2 +-
|  1 files changed, 1 insertions(+), 1 deletions(-)
| 
| diff --git a/mm/slob.c b/mm/slob.c
| index ff5a98d..dce9258 100644
| --- a/mm/slob.c
| +++ b/mm/slob.c
| @@ -538,7 +538,7 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
|  	struct kmem_cache *c;
|  
|  	c = slob_alloc(sizeof(struct kmem_cache),
| -		flags, ARCH_KMALLOC_MINALIGN, -1);
| +		GFP_KERNEL, ARCH_KMALLOC_MINALIGN, -1);
|  
|  	if (c) {
|  		c->name = name;
|

Hi Catalin,

this would make the following line in slob_alloc

	...
	if (unlikely((gfp & __GFP_ZERO) && b))
		memset(b, 0, size);
 	...

useless. Not sure if it will be good :)

---
Some  CC: added

		- Cyrill -

Re: [PATCH] Do not pass the SLAB flags as GFP in slob kmem_cache_create

[Matt Mackall]

On Wed, 2008-12-10 at 22:34 +0300, Cyrill Gorcunov wrote:
> [Catalin Marinas - Wed, Dec 10, 2008 at 05:36:33PM +0000]
> | It looks like the kmem_cache_create() function in the slob allocator
> | passes the SLAB flags as GFP flags to the slob_alloc() function. The
> | patch changes this call to pass GFP_KERNEL as the other allocators seem
> | to do.
> | 
> | Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> | Cc: Matt Mackall <mpm@selenic.com>
> | ---
> |  mm/slob.c |    2 +-
> |  1 files changed, 1 insertions(+), 1 deletions(-)
> | 
> | diff --git a/mm/slob.c b/mm/slob.c
> | index ff5a98d..dce9258 100644
> | --- a/mm/slob.c
> | +++ b/mm/slob.c
> | @@ -538,7 +538,7 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
> |  	struct kmem_cache *c;
> |  
> |  	c = slob_alloc(sizeof(struct kmem_cache),
> | -		flags, ARCH_KMALLOC_MINALIGN, -1);
> | +		GFP_KERNEL, ARCH_KMALLOC_MINALIGN, -1);
> |  
> |  	if (c) {
> |  		c->name = name;
> |
> 
> Hi Catalin,
> 
> this would make the following line in slob_alloc
> 
> 	...
> 	if (unlikely((gfp & __GFP_ZERO) && b))
> 		memset(b, 0, size);
>  	...
> 
> useless. Not sure if it will be good :)

I think that's fine. Notice that this is not the allocation of an
object, but the allocation of a cache descriptor. We save the flags
inside the descriptor so that when the user calls kmem_cache_alloc, we
can pass them along to slob_alloc, where GFP_ZERO can take effect.

So, if we're comfortable with the idea that we can only create caches in
'normal' contexts, then I think the patch is fine.

-- 
Mathematics is the supreme nostalgia of our time.

Re: [PATCH] Do not pass the SLAB flags as GFP in slob kmem_cache_create

[Cyrill Gorcunov]

[Matt Mackall - Wed, Dec 10, 2008 at 01:57:50PM -0600]
... 
| I think that's fine. Notice that this is not the allocation of an
| object, but the allocation of a cache descriptor. We save the flags
| inside the descriptor so that when the user calls kmem_cache_alloc, we
| can pass them along to slob_alloc, where GFP_ZERO can take effect.
| 
| So, if we're comfortable with the idea that we can only create caches in
| 'normal' contexts, then I think the patch is fine.
| 
| -- 
| Mathematics is the supreme nostalgia of our time.
| 

Yes Matt, somehow missed that.

		- Cyrill -

Re: [PATCH] Do not pass the SLAB flags as GFP in slob kmem_cache_create

[Christoph Lameter]

On Wed, 10 Dec 2008, Cyrill Gorcunov wrote:

> this would make the following line in slob_alloc
>
> 	...
> 	if (unlikely((gfp & __GFP_ZERO) && b))
> 		memset(b, 0, size);
>  	...
>
> useless. Not sure if it will be good :)

No. GFP_ZERO is set when kmalloc etc is called. Its not set on
kmem_cache_create.

Re: [PATCH] Do not pass the SLAB flags as GFP in slob kmem_cache_create

[Cyrill Gorcunov]

[Christoph Lameter - Wed, Dec 10, 2008 at 02:11:23PM -0600]
| On Wed, 10 Dec 2008, Cyrill Gorcunov wrote:
| 
| > this would make the following line in slob_alloc
| >
| > 	...
| > 	if (unlikely((gfp & __GFP_ZERO) && b))
| > 		memset(b, 0, size);
| >  	...
| >
| > useless. Not sure if it will be good :)
| 
| No. GFP_ZERO is set when kmalloc etc is called. Its not set on
| kmem_cache_create.
| 

yep, Matt already pointed, I just missed first time.

		- Cyrill -

Re: [PATCH] Do not pass the SLAB flags as GFP in slob kmem_cache_create

[Matt Mackall]

On Wed, 2008-12-10 at 17:36 +0000, Catalin Marinas wrote:
> It looks like the kmem_cache_create() function in the slob allocator
> passes the SLAB flags as GFP flags to the slob_alloc() function. The
> patch changes this call to pass GFP_KERNEL as the other allocators seem
> to do.
> 
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Matt Mackall <mpm@selenic.com>

Good catch.

Acked-by: Matt Mackall <mpm@selenic.com>

-- 
Mathematics is the supreme nostalgia of our time.

Re: [PATCH] Do not pass the SLAB flags as GFP in slob kmem_cache_create

[Pekka Enberg]

On Wed, Dec 10, 2008 at 7:36 PM, Catalin Marinas
<catalin.marinas@arm.com> wrote:
> It looks like the kmem_cache_create() function in the slob allocator
> passes the SLAB flags as GFP flags to the slob_alloc() function. The
> patch changes this call to pass GFP_KERNEL as the other allocators seem
> to do.
>
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Matt Mackall <mpm@selenic.com>

Applied, thanks!