We can create shared anonymous memory via "-object memory-backend-ram,share=on,..." which is, for example, required by PVRDMA for mremap() to work.
Shared anonymous memory is weird, though. Instead of MADV_DONTNEED, we have to use MADV_REMOVE. MADV_DONTNEED fails silently and does nothing. Fixes: 06329ccecfa0 ("mem: add share parameter to memory-backend-ram") Signed-off-by: David Hildenbrand <da...@redhat.com> --- softmmu/physmem.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/softmmu/physmem.c b/softmmu/physmem.c index 62ea4abbdd..2ba815fec6 100644 --- a/softmmu/physmem.c +++ b/softmmu/physmem.c @@ -3506,6 +3506,7 @@ int ram_block_discard_range(RAMBlock *rb, uint64_t start, size_t length) /* The logic here is messy; * madvise DONTNEED fails for hugepages * fallocate works on hugepages and shmem + * shared anonymous memory requires madvise REMOVE */ need_madvise = (rb->page_size == qemu_host_page_size); need_fallocate = rb->fd != -1; @@ -3539,7 +3540,11 @@ int ram_block_discard_range(RAMBlock *rb, uint64_t start, size_t length) * fallocate'd away). */ #if defined(CONFIG_MADVISE) - ret = madvise(host_startaddr, length, MADV_DONTNEED); + if (qemu_ram_is_shared(rb) && rb->fd < 0) { + ret = madvise(host_startaddr, length, MADV_REMOVE); + } else { + ret = madvise(host_startaddr, length, MADV_DONTNEED); + } if (ret) { ret = -errno; error_report("ram_block_discard_range: Failed to discard range " -- 2.29.2