2007/7/25, Shaohua Li <[EMAIL PROTECTED]>:
2007/7/24, Avi Kivity <[EMAIL PROTECTED]>:
> Shaohua Li wrote:
> > Make KVM guest pages be allocated dynamically and able to be swaped out.
> >
> > One issue: all inodes returned from anon_inode_getfd are shared,
> > if one module changes field of the inode, other moduels might break.
> > Should we introduce a new API to not share inode?
> >
> > Signed-off-by: Shaohua Li <[EMAIL PROTECTED]>
> > ---
> >
> > +static int kvm_set_page_dirty(struct page *page)
> > +{
> > + if (!PageDirty(page))
> > + SetPageDirty(page);
> > + return 0;
> > +}
> > +
> > +static int kvm_writepage(struct page *page, struct writeback_control *wbc)
> > +{
> > + struct address_space *mapping = page->mapping;
> > + struct kvm *kvm = address_space_to_kvm(mapping);
> > + int ret = 0;
> > +
> > + /*
> > + * gfn_to_page is called with kvm->lock hold, which might invoke page
> > + * reclaim. So the .writepage should check if we already hold the lock
> > + * to avoid deadlock.
> > + */
> > + if (!mutex_trylock(&kvm->lock)) {
> > + set_page_dirty(page);
> > + return AOP_WRITEPAGE_ACTIVATE;
> > + }
> > +
> > + /*
> > + * We just zap vcpu 0's page table. For a SMP guest, we should zap all
> > + * vcpus'. It's better shadow page table is per-vm.
> > + */
> > + if (PagePrivate(page))
> > + kvm_mmu_zap_pagetbl(&kvm->vcpus[0], page->index);
> > +
> > + ret = kvm_move_to_swap(page);
> > + if (ret) {
> > + set_page_dirty(page);
> > + goto out;
> > + }
> > + unlock_page(page);
> > +out:
> > + mutex_unlock(&kvm->lock);
> > +
> > + return ret;
> > +}
> > +
> >
>
> Perhaps we can use this as a base for userspace-allocated memory. We
> still have a kvm inode and address_space; but instead of calling
> kvm_move_to_swap(), we use the memory slot and virtual address offset to
> locate the underlying address_space and call that ->writepage().
>
> So:
> kvm_writepage() removes any shadow page table references
> the underlying ->writepage() does the work of paging to the underlying
> store
So write to a file, right? Yes, it can avoid use move to swap, and
should be feasible.
Say you want to write guest pages out to file A of back store fs, in
kvm->writepage(), we could do:
1. lower_page = grap_cache_page(file A's mapping)
2. file A's ->prepare_write(lower_page)
3. copy kvm guest page to lower_page
4. file A's ->commit_write(lower_page)
then guest page can be freed. Just like the stack fs does. The
downside is step 1 needs allocate a new page.
Thanks,
Shaohua
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