On Fri, Mar 4, 2011 at 11:33 AM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
>
> So I assumed the slab allocator would hold a reference to the page like
> any other user would, in which case the tcp code could take a second
> reference of its own.
So the reason that wouldn't work is simple: the reference is obviously
at a page level, but slab doles out allocations on its own level.
What does that mean? Imagine if the network layer takes a ref on the
page, but then the original user does a "kfree()". The _page_ would
stay around (we have a ref from it - but so does the slab allocator),
but the thing is, the slab allocator will release and then re-use the
slab entry.
So the "hold a reference to the page" doesn't actually _help_. The
problem isn't the page going away, it's the smaller slab-allocation
being reused for something else - so the page-level ref would be
useless.
So page-level references really only do work with page allocators.
They don't know about the allocation patterns within a page that slab
does.
Linus
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