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block_util: Avoid reallocation of Vec on push

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When using DHAT[1] for analysis the amount heap allocations change from:

dhat: Total:     3,186,536 bytes in 41,452 blocks

 to

dhat: Total:     1,059,816 bytes in 34,747 blocks

When running against virtio-block; this still more allocations than
virtio-pmem but a significant improvement without any cost.

[1] https://docs.rs/dhat/latest/dhat/

Signed-off-by: Rob Bradford <robert.bradford@intel.com>
This commit is contained in:
Rob Bradford 2023-01-09 17:39:43 +00:00 committed by Bo Chen
parent 9e8296b696
commit eb87538100
2 changed files with 3 additions and 3 deletions
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3
block_util/src/lib.rs
View File

@ -249,6 +249,7 @@ impl Request {
return Err(Error::DescriptorChainTooShort);
}
} else {
req.data_descriptors.reserve_exact(1);
while desc.has_next() {
if desc.is_write_only() && req.request_type == RequestType::Out {
return Err(Error::UnexpectedWriteOnlyDescriptor);
@ -353,7 +354,7 @@ impl Request {
let request_type = self.request_type;
let offset = (sector << SECTOR_SHIFT) as libc::off_t;
let mut iovecs = Vec::new();
let mut iovecs = Vec::with_capacity(self.data_descriptors.len());
for (data_addr, data_len) in &self.data_descriptors {
if *data_len == 0 {
continue;

3
block_util/src/raw_async.rs
View File

@ -156,9 +156,8 @@ impl AsyncIo for RawFileAsync {
}
fn complete(&mut self) -> Vec<(u64, i32)> {
let mut completion_list = Vec::new();
let cq = self.io_uring.completion();
let mut completion_list = Vec::with_capacity(cq.len());
for cq_entry in cq {
completion_list.push((cq_entry.user_data(), cq_entry.result()));
}