* David Hildenbrand (da...@redhat.com) wrote:
> 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.
OK, I wonder how stable these rules are; is it defined anywhere that
it's required?
Still,
Reviewed-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
> 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
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
