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block: increase the size of temporary vectors

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The size was set to one because without VIRTIO_BLK_F_SEG_MAX, the guest
only used one data descriptor per request.

The value 32 is empirically derived from booting a guest. This value
eliminates all SmallVec allocations observable by DHAT.

Signed-off-by: Wei Liu <liuwe@microsoft.com>
This commit is contained in:
Wei Liu 2024-12-21 00:54:15 +00:00
parent d0a1171870
commit 0e72d9b5ed
1 changed files with 11 additions and 7 deletions
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18
block/src/lib.rs
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@ -220,6 +220,8 @@ fn sector<B: Bitmap + 'static>(
mem.read_obj(addr).map_err(Error::GuestMemory)
}
const DEFAULT_DESCRIPTOR_VEC_SIZE: usize = 32;
#[derive(Debug)]
pub struct AlignedOperation {
origin_ptr: u64,
@ -232,10 +234,10 @@ pub struct AlignedOperation {
pub struct Request {
pub request_type: RequestType,
pub sector: u64,
pub data_descriptors: SmallVec<[(GuestAddress, u32); 1]>,
pub data_descriptors: SmallVec<[(GuestAddress, u32); DEFAULT_DESCRIPTOR_VEC_SIZE]>,
pub status_addr: GuestAddress,
pub writeback: bool,
pub aligned_operations: SmallVec<[AlignedOperation; 1]>,
pub aligned_operations: SmallVec<[AlignedOperation; DEFAULT_DESCRIPTOR_VEC_SIZE]>,
pub start: Instant,
}
@ -263,10 +265,10 @@ impl Request {
let mut req = Request {
request_type: request_type(desc_chain.memory(), hdr_desc_addr)?,
sector: sector(desc_chain.memory(), hdr_desc_addr)?,
data_descriptors: SmallVec::with_capacity(1),
data_descriptors: SmallVec::with_capacity(DEFAULT_DESCRIPTOR_VEC_SIZE),
status_addr: GuestAddress(0),
writeback: true,
aligned_operations: SmallVec::with_capacity(1),
aligned_operations: SmallVec::with_capacity(DEFAULT_DESCRIPTOR_VEC_SIZE),
start: Instant::now(),
};
@ -398,7 +400,7 @@ impl Request {
let request_type = self.request_type;
let offset = (sector << SECTOR_SHIFT) as libc::off_t;
let mut iovecs: SmallVec<[libc::iovec; 1]> =
let mut iovecs: SmallVec<[libc::iovec; DEFAULT_DESCRIPTOR_VEC_SIZE]> =
SmallVec::with_capacity(self.data_descriptors.len());
for (data_addr, data_len) in &self.data_descriptors {
if *data_len == 0 {
@ -653,7 +655,8 @@ where
completion_list: &mut VecDeque<(u64, i32)>,
) -> AsyncIoResult<()> {
// Convert libc::iovec into IoSliceMut
let mut slices: SmallVec<[IoSliceMut; 1]> = SmallVec::with_capacity(iovecs.len());
let mut slices: SmallVec<[IoSliceMut; DEFAULT_DESCRIPTOR_VEC_SIZE]> =
SmallVec::with_capacity(iovecs.len());
for iovec in iovecs.iter() {
// SAFETY: on Linux IoSliceMut wraps around libc::iovec
slices.push(IoSliceMut::new(unsafe {
@ -690,7 +693,8 @@ where
completion_list: &mut VecDeque<(u64, i32)>,
) -> AsyncIoResult<()> {
// Convert libc::iovec into IoSlice
let mut slices: SmallVec<[IoSlice; 1]> = SmallVec::with_capacity(iovecs.len());
let mut slices: SmallVec<[IoSlice; DEFAULT_DESCRIPTOR_VEC_SIZE]> =
SmallVec::with_capacity(iovecs.len());
for iovec in iovecs.iter() {
// SAFETY: on Linux IoSlice wraps around libc::iovec
slices.push(IoSlice::new(unsafe {