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vmm: Refine the granularity of dirty memory tracking

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Instead of tracking on a block level of 64 pages, we are now collecting
dirty pages one by one. It improves the efficiency of dirty memory
tracking while live migration.

Signed-off-by: Bo Chen <chen.bo@intel.com>
This commit is contained in:
Bo Chen 2021-04-16 17:30:29 -07:00 committed by Sebastien Boeuf
parent 4c299c6c00
commit 78796f96b7
1 changed files with 16 additions and 34 deletions
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50
vmm/src/memory_manager.rs
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@ -1493,25 +1493,13 @@ impl MemoryManager {
&self.memory_zones
}
// Generate a table for the pages that are dirty. The algorithm is currently
// very simple. If any page in a "block" of 64 pages is dirty then that whole
// "block" is added to the table. These "blocks" are also collapsed together if
// they are contiguous:
//
// For every block of 64 pages we check to see if there are any dirty pages in it
// if there are we increase the size of the current range if there is one, otherwise
// create a new range. If there are no dirty pages in the current "block" the range is
// closed if there is one and added to the table. After iterating through the dirty
// page bitmaps an open range will be closed and added to the table.
//
// This algorithm is very simple and could be refined to count the number of pages
// in the block and instead create smaller ranges covering those pages.
// Generate a table for the pages that are dirty. The dirty pages are collapsed
// together in the table if they are contiguous.
pub fn dirty_memory_range_table(
&self,
) -> std::result::Result<MemoryRangeTable, MigratableError> {
let page_size = 4096; // TODO: Does this need to vary?
let mut table = MemoryRangeTable::default();
let mut total_pages = 0;
for r in &self.guest_ram_mappings {
let dirty_bitmap = self.vm.get_dirty_log(r.slot, r.size).map_err(|e| {
MigratableError::MigrateSend(anyhow!("Error getting VM dirty log {}", e))
@ -1519,18 +1507,21 @@ impl MemoryManager {
let mut entry: Option<MemoryRange> = None;
for (i, block) in dirty_bitmap.iter().enumerate() {
if *block > 0 {
if let Some(entry) = &mut entry {
entry.length += 64 * page_size;
} else {
entry = Some(MemoryRange {
gpa: r.gpa + (64 * i as u64 * page_size),
length: 64 * page_size,
});
for j in 0..64 {
let is_page_dirty = ((block >> j) & 1u64) != 0u64;
let page_offset = ((i * 64) + j) as u64 * page_size;
if is_page_dirty {
if let Some(entry) = &mut entry {
entry.length += page_size;
} else {
entry = Some(MemoryRange {
gpa: r.gpa + page_offset,
length: page_size,
});
}
} else if let Some(entry) = entry.take() {
table.push(entry);
}
total_pages += block.count_ones() as u64;
} else if let Some(entry) = entry.take() {
table.push(entry);
}
}
if let Some(entry) = entry.take() {
@ -1541,18 +1532,9 @@ impl MemoryManager {
info!("Dirty Memory Range Table is empty");
} else {
info!("Dirty Memory Range Table:");
let mut total_size = 0;
for range in table.regions() {
info!("GPA: {:x} size: {} (KiB)", range.gpa, range.length / 1024);
total_size += range.length;
}
info!(
"Total pages: {} ({} KiB). Total size: {} KiB. Efficiency: {}%",
total_pages,
total_pages * page_size / 1024,
total_size / 1024,
(total_pages * page_size * 100) / total_size
);
}
}
Ok(table)