On Thu, 17 Nov 2005, Ingo Oeser wrote:
>
> We do we refcount ZERO_PAGE at all?
We never used to. They were, and for the moment still are, marked
PageReserved. Prior to 2.6.15-rc we didn't refcount reserved pages,
but now we're trying to move away from PageReserved (some differences
of opinion how far to go), so refcounting them.
We're currently refcounting the ZERO_PAGE(s) simply because the
common case is refcounted: it would just be extra tests and code
NOT to refcount the ZERO_PAGE(s). If they were a commoner case,
then it would indeed be worth avoiding refcounting them, but it
currently doesn't appear to be worth the effort.
But it is still up in the air: there is or may be an issue with
refcounts overflowing, and if it's clear that the ZERO_PAGE is
the only one vulnerable on any architecture, then I'm sure we'd
deal with it by not refcounting them. However, I believe the
issue extends to mapped file pages too: though you need a huge
amount of RAM to reach overflow, so it's not something we need
to resolve this week.
> Ok, there may be multiple, but they exist always and always at
> the same physical addresses, right?
Right.
> So why do we care at all?
> Memory hotplug?
> Doesn't it suffice there, that they are reverse mappable?
Actually, they're not reverse mappable: we tend to find
there's not much gained by swapping out the ZERO_PAGE ;)
Hugh
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]