On 7/27/2020 1:11 PM, Anthony Yznaga wrote: > This patchset adds support for preserving an anonymous memory range across > exec(3) using a new madvise MADV_DOEXEC argument. The primary benefit for > sharing memory in this manner, as opposed to re-attaching to a named shared > memory segment, is to ensure it is mapped at the same virtual address in > the new process as it was in the old one. An intended use for this is to > preserve guest memory for guests using vfio while qemu exec's an updated > version of itself. By ensuring the memory is preserved at a fixed address, > vfio mappings and their associated kernel data structures can remain valid. > In addition, for the qemu use case, qemu instances that back guest RAM with > anonymous memory can be updated.
I forgot to mention, our use case is not just theoretical. It has been implemented and is pretty cool (but I am biased). The pause time for the guest is in the 100 - 200 msec range. We submitted qemu patches for review based on the MADV_DOEXEC proposal. In case you are curious: https://lore.kernel.org/qemu-devel/1596122076-341293-1-git-send-email-steven.sist...@oracle.com/ - Steve
