Eliminate an unnecessary parameter to kmem_malloc_domain()

[alc]

Summary

The arena parameter to kmem_malloc_domain() is unnecessary. The domain and flags parameters suffice. In fact, the related functions kmem_alloc_{attr,contig}_domain() don't have this parameter.

The above stylistic argument aside, my real motivation for making this change now is that I want to implement stronger segregation for the physical memory that backs UMA _NOFREE zones. (See D16620 for a hackish proof-of-concept.) And, I don't want to have to modify affected kmem_malloc_domain() callers to pass in yet a different arena, when that parameter really serves no purpose.

[markj]

Do you plan to update the kmem_malloc() prototype at some point?

[alc]

In D16713#355831, @markj wrote:

Do you plan to update the kmem_malloc() prototype at some point?

I would happily see the arena argument removed from all of these functions before we branch 12.x. kmem_free() is the only one where the arena isn't entirely redundant. Essentially, kmem_free() uses the arena as a flag to determine whether the addresses should be returned to the domain's kernel arena or rwx arena.

Do we have a consensus?

[markj]

In D16713#355892, @alc wrote:

In D16713#355831, @markj wrote:

Do you plan to update the kmem_malloc() prototype at some point?

I would happily see the arena argument removed from all of these functions before we branch 12.x. kmem_free() is the only one where the arena isn't entirely redundant. Essentially, kmem_free() uses the arena as a flag to determine whether the addresses should be returned to the domain's kernel arena or rwx arena.

Do we have a consensus?

Are you proposing that we keep the arena parameter to kmem_free()? I'd rather see it converted to a set of malloc flags (with M_EXEC being the only valid flag for now). Either way, I'd also be happy to remove the arena argument from the other functions.

[alc]

In D16713#355903, @markj wrote:

In D16713#355892, @alc wrote:

In D16713#355831, @markj wrote:

Do you plan to update the kmem_malloc() prototype at some point?

I would happily see the arena argument removed from all of these functions before we branch 12.x. kmem_free() is the only one where the arena isn't entirely redundant. Essentially, kmem_free() uses the arena as a flag to determine whether the addresses should be returned to the domain's kernel arena or rwx arena.

Do we have a consensus?

Are you proposing that we keep the arena parameter to kmem_free()?

No.

I'd rather see it converted to a set of malloc flags (with M_EXEC being the only valid flag for now). Either way, I'd also be happy to remove the arena argument from the other functions.

Alternatively, we could avoid the need for a flags parameter by marking the pages. I would compare this to the way that kmem_free() recovers the domain to which it should return the addresses.

[markj]

In D16713#355911, @alc wrote:

In D16713#355903, @markj wrote:

I'd rather see it converted to a set of malloc flags (with M_EXEC being the only valid flag for now). Either way, I'd also be happy to remove the arena argument from the other functions.

Alternatively, we could avoid the need for a flags parameter by marking the pages. I would compare this to the way that kmem_free() recovers the domain to which it should return the addresses.

I'm a bit hesitant about the idea of marking the physical page to reflect a property of its mapping, but I think that approach would work fine too.