On Mon, Apr 23, 2018 at 12:59 AM Christian Borntraeger <
borntraeger@xxxxxxxxxx> wrote:
> On 04/23/2018 09:41 AM, Christian Borntraeger wrote:
> >
> >
> > On 04/21/2018 12:07 AM, Marc Orr wrote:
> >> First off---thanks for reviewing my patch!
> >>
> >> With respect to the size of the struct, here's what I'm seeing on an
> >> upstream
> >> version of the kernel:
> >>
> >> (gdb) p sizeof(struct kvm)
> >> $1 = 42200
> >> (gdb) p sizeof(struct kvm_arch)
> >> $2 = 35496
> >
> > Yes, I looked at an older kernel on x86. Sorry about that. The newer
kernels
> > certainly have grown. Would be interesting to see why. Can you run
> > pahole (usually in the package dwarves) on you kernel and search for
> > "struct kvm "
> Seems to be
> struct hlist_head mmu_page_hash[4096]; /* 24 32768 */
> in kvm_arch.
> This is now much larger mostly due to
> commit 114df303a7eeae8b50ebf68229b7e647714a9bea
> kvm: x86: reduce collisions in mmu_page_hash
> So maybe it is enough to allocate mmu_page_hash seperately? Adding David
Matlack
> for opinions.
Allocating mmu_page_hash separately would not create any issues I can think
of. But Mark's concern about future bloat still remains.
One option to move forward would be to make this change x86-specific by
overriding kvm_arch_{alloc,free}_vm. Other architectures could do the same
once they check that it's safe.
