On 05.08.21 10:21, Philippe Mathieu-Daudé wrote:
On 8/5/21 10:11 AM, David Hildenbrand wrote:
On 05.08.21 10:04, Philippe Mathieu-Daudé wrote:
On 7/30/21 10:52 AM, David Hildenbrand wrote:
We already don't ever migrate memory that corresponds to discarded
ranges
as managed by a RamDiscardManager responsible for the mapped memory
region
of the RAMBlock.
virtio-mem uses this mechanism to logically unplug parts of a RAMBlock.
Right now, we still populate zeropages for the whole usable part of the
RAMBlock, which is undesired because:
1. Even populating the shared zeropage will result in memory getting
consumed for page tables.
2. Memory backends without a shared zeropage (like hugetlbfs and shmem)
will populate an actual, fresh page, resulting in an unintended
memory consumption.
Discarded ("logically unplugged") parts have to remain discarded. As
these pages are never part of the migration stream, there is no need to
track modifications via userfaultfd WP reliably for these parts.
Further, any writes to these ranges by the VM are invalid and the
behavior is undefined.
Note that Linux only supports userfaultfd WP on private anonymous memory
for now, which usually results in the shared zeropage getting populated.
The issue will become more relevant once userfaultfd WP supports shmem
and hugetlb.
Acked-by: Peter Xu <pet...@redhat.com>
Signed-off-by: David Hildenbrand <da...@redhat.com>
---
migration/ram.c | 53 +++++++++++++++++++++++++++++++++++++++++--------
1 file changed, 45 insertions(+), 8 deletions(-)
diff --git a/migration/ram.c b/migration/ram.c
index 01cea01774..fd5949734e 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1639,6 +1639,28 @@ out:
return ret;
}
+static inline void populate_range(RAMBlock *block, hwaddr offset,
hwaddr size)
+{
+ char *ptr = (char *) block->host;
+
+ for (; offset < size; offset += ) {
+ char tmp = *(ptr + offset);
+
+ /* Don't optimize the read out */
+ asm volatile("" : "+r" (tmp));
+ }
This template is now used 3 times, a good opportunity to extract it as
an (inline?) helper.
Can you point me at the other users?
Oops I got lost reviewing the series.
Isn't populate_range() the inline helper you are looking for? :)
Indeed :)
Being a bit picky, I'd appreciate if you split this patch in 2,
extracting populate_range() as a first trivial step.
Will do, and while at it again, will use ram_addr_t for the parameters
and block->page_size instead of qemu_real_host_page_size.
--
Thanks,
David / dhildenb
