On 12.02.20 14:35, David Hildenbrand wrote: > We already allow resizable ram blocks for anonymous memory, however, they > are not actually resized. All memory is mmaped() R/W, including the memory > exceeding the used_length, up to the max_length. > > When resizing, effectively only the boundary is moved. Implement actually > resizable anonymous allocations and make use of them in resizable ram > blocks when possible. Memory exceeding the used_length will be > inaccessible. Especially ram block notifiers require care. > > Having actually resizable anonymous allocations (via mmap-hackery) allows > to reserve a big region in virtual address space and grow the > accessible/usable part on demand. Even if "/proc/sys/vm/overcommit_memory" > is set to "never" under Linux, huge reservations will succeed. If there is > not enough memory when resizing (to populate parts of the reserved region), > trying to resize will fail. Only the actually used size is reserved in the > OS. > > E.g., virtio-mem [1] wants to reserve big resizable memory regions and > grow the usable part on demand. I think this change is worth sending out > individually. Accompanied by a bunch of minor fixes and cleanups. > > Especially, memory notifiers already handle resizing by first removing > the old region, and then re-adding the resized region. prealloc is > currently not possible with resizable ram blocks. mlock() should continue > to work as is. Resizing is currently rare and must only happen on the > start of an incoming migration, or during resets. No code path (except > HAX and SEV ram block notifiers) should access memory outside of the usable > range - and if we ever find one, that one has to be fixed (I did not > identify any). > > v1 -> v2: > - Add "util: vfio-helpers: Fix qemu_vfio_close()" > - Add "util: vfio-helpers: Remove Error parameter from > qemu_vfio_undo_mapping()" > - Add "util: vfio-helpers: Factor out removal from > qemu_vfio_undo_mapping()" > - "util/mmap-alloc: ..." > -- Minor changes due to review feedback (e.g., assert alignment, return > bool when resizing) > - "util: vfio-helpers: Implement ram_block_resized()" > -- Reserve max_size in the IOVA address space. > -- On resize, undo old mapping and do new mapping. We can later implement > a new ioctl to resize the mapping directly. > - "numa: Teach ram block notifiers about resizable ram blocks" > -- Pass size/max_size to ram block notifiers, which makes things easier an > cleaner > - "exec: Ram blocks with resizable anonymous allocations under POSIX" > -- Adapt to new ram block notifiers > -- Shrink after notifying. Always trigger ram block notifiers on resizes > -- Add a safety net that all ram block notifiers registered at runtime > support resizes. > > [1] https://lore.kernel.org/kvm/20191212171137.13872-1-da...@redhat.com/ > > David Hildenbrand (16): > util: vfio-helpers: Factor out and fix processing of existing ram > blocks > util: vfio-helpers: Fix qemu_vfio_close() > util: vfio-helpers: Remove Error parameter from > qemu_vfio_undo_mapping() > util: vfio-helpers: Factor out removal from qemu_vfio_undo_mapping() > exec: Factor out setting ram settings (madvise ...) into > qemu_ram_apply_settings() > exec: Reuse qemu_ram_apply_settings() in qemu_ram_remap() > exec: Drop "shared" parameter from ram_block_add() > util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize() > util/mmap-alloc: Factor out reserving of a memory region to > mmap_reserve() > util/mmap-alloc: Factor out populating of memory to mmap_populate() > util/mmap-alloc: Prepare for resizable mmaps > util/mmap-alloc: Implement resizable mmaps > numa: Teach ram block notifiers about resizable ram blocks > util: vfio-helpers: Implement ram_block_resized() > util: oslib: Resizable anonymous allocations under POSIX > exec: Ram blocks with resizable anonymous allocations under POSIX
I should double check what I send out while doing last minute changes. Please ignore this series, will send the proper one right away. -- Thanks, David / dhildenb
