* David Hildenbrand (da...@redhat.com) wrote: > On 12.02.20 14:42, 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 > > > > exec.c | 104 +++++++++++++++++++---- > > hw/core/numa.c | 53 +++++++++++- > > hw/i386/xen/xen-mapcache.c | 7 +- > > include/exec/cpu-common.h | 3 + > > include/exec/memory.h | 8 ++ > > include/exec/ramlist.h | 14 +++- > > include/qemu/mmap-alloc.h | 21 +++-- > > include/qemu/osdep.h | 6 +- > > stubs/ram-block.c | 20 ----- > > target/i386/hax-mem.c | 5 +- > > target/i386/sev.c | 18 ++-- > > util/mmap-alloc.c | 165 +++++++++++++++++++++++-------------- > > util/oslib-posix.c | 37 ++++++++- > > util/oslib-win32.c | 14 ++++ > > util/trace-events | 9 +- > > util/vfio-helpers.c | 145 +++++++++++++++++++++----------- > > 16 files changed, 450 insertions(+), 179 deletions(-) > > > > 1. I will do resizable -> resizeable > 2. I think migration might indeed need some care regarding > max_length. We should never migrate anything beyond used_length. And > if we receive something, it should be discarded. Will look into that.
It feels like we should warn/error if we receive something beyond used? Dave > -- > Thanks, > > David / dhildenb -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK