Messages in this thread |  | | | Date | Wed, 25 Jul 2007 21:20:17 +0800 | | From | "Shaohua Li" <> | | Subject | Re: [kvm-devel] [RFC 7/8]KVM: swap out guest pages |
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2007/7/25, Shaohua Li <shaoh.li@gmail.com>: > 2007/7/24, Avi Kivity <avi@qumranet.com>: > > 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 > 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.
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