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Re: [PATCH v5] slab: Ignore internal flags in cache creation [message #48504 is a reply to message #48424] Thu, 18 October 2012 22:42 Go to previous messageGo to previous message
akpm is currently offline  akpm
Messages: 224
Registered: March 2007
Senior Member
On Wed, 17 Oct 2012 15:36:51 +0400
Glauber Costa <glommer@parallels.com> wrote:

> Some flags are used internally by the allocators for management
> purposes. One example of that is the CFLGS_OFF_SLAB flag that slab uses
> to mark that the metadata for that cache is stored outside of the slab.
>
> No cache should ever pass those as a creation flags. We can just ignore
> this bit if it happens to be passed (such as when duplicating a cache in
> the kmem memcg patches).

I may be minunderstanding this, but...

If some caller to kmem_cache_create() is passing in bogus flags then
that's a bug, and it is undesirable to hide such a bug in this fashion?

> Because such flags can vary from allocator to allocator, we allow them
> to make their own decisions on that, defining SLAB_AVAILABLE_FLAGS with
> all flags that are valid at creation time. Allocators that doesn't have
> any specific flag requirement should define that to mean all flags.
>
> Common code will mask out all flags not belonging to that set.

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