Messages in this thread | | | Date | Tue, 24 Jul 2007 17:55:04 +0300 | From | Avi Kivity <> | Subject | Re: [RFC 7/8]KVM: swap out guest pages |
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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 <shaohua.li@intel.com> > --- > > +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
We need to figure out how to avoid the underlying ->writepage() from not within the context of kvm_writepage(). Maybe have a page flag signifying layered address spaces?
[it probably violates fifteen different mm assumptions; I need to study that code]
An alternative would be to have kvm set a page flag signifying it has references to the page when it installs it in a shadow pte. The mm would notice the flag and call kvm to clear it below proceeding with normal ->writepage().
-- error compiling committee.c: too many arguments to function
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