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feat: optimize allocations in writable CoW accounts #4846

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bmuddha wants to merge 3 commits into from
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feat: optimize allocations in writable CoW accounts #4846

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f49726d
feat: optimize allocations in writable CoW accounts
bmuddha Feb 7, 2025
f335628
Merge branch 'master' into realloc-optimization
bmuddha Feb 7, 2025
c18ac16
fix: use saturating_sub in delta capacity calculation
bmuddha Feb 7, 2025
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5 changes: 0 additions & 5 deletions programs/bpf_loader/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -265,11 +265,6 @@ fn create_vm<'a, 'b>(
.touch(index_in_transaction as IndexOfAccount)
.map_err(|_| ())?;

if account.is_shared() {
// See BorrowedAccount::make_data_mut() as to why we reserve extra
// MAX_PERMITTED_DATA_INCREASE bytes here.
account.reserve(MAX_PERMITTED_DATA_INCREASE);
}
Ok(account.data_as_mut_slice().as_mut_ptr() as u64)
})),
)?;
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7 changes: 7 additions & 0 deletions programs/bpf_loader/src/serialization.rs
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Expand Up @@ -579,6 +579,13 @@ fn deserialize_parameters_aligned<I: IntoIterator<Item = usize>>(
borrowed_account.set_data_length(post_len)?;
let allocated_bytes = post_len.saturating_sub(pre_len);
if allocated_bytes > 0 {
// Just in time resize of data field within the internal AccountSharedData
//
// NOTE: this is an optimization for CoW account mappings, where the account's
// data is not immediately resized with an extra MAX_PERMITTED_DATA_INCREASE,
// but if the realloc did occur (and this branch was taken) then we need to reserve
// max permitted amount of extra space so the subsequent code will work correctly
borrowed_account.reserve(MAX_PERMITTED_DATA_INCREASE)?;
borrowed_account
.get_data_mut()?
.get_mut(pre_len..pre_len.saturating_add(allocated_bytes))
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10 changes: 6 additions & 4 deletions sdk/transaction-context/src/lib.rs
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Expand Up @@ -974,7 +974,12 @@ impl BorrowedAccount<'_> {
// memory that holds the account but it doesn't actually change content
// nor length of the account.
self.make_data_mut();
self.account.reserve(additional);
// NOTE: we don't call reserve unnecessarily, as the first call to make_data_mut
// has already resized the data to an extra MAX_PERMITTED_DATA_INCREASE bytes
if additional > MAX_PERMITTED_DATA_INCREASE {
self.account
.reserve(additional.saturating_sub(MAX_PERMITTED_DATA_INCREASE));
}
Comment on lines +979 to +982
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@ceciEstErmat ceciEstErmat Feb 20, 2025

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I know it was previously already the case and this condition just makes it better but the double reallocation does feel like a big waste. Especially in such case where the data size is know to be pretty big already.
I wonder if the introduction of a "make mut with additional size" or something of the sort would be acceptable.

Also i'm unsure if it is actually possible for additional to be > MAX_PERMITTED_DATA_INCREASE but since its been renamed from MAX_PERMITTED_DATA_LENGTH it may now/soon be the case.

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@ceciEstErmat ceciEstErmat Feb 20, 2025

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But overall feels like a very positive change - everything that can speed up execution is more than welcomed...


Ok(())
}
Expand Down Expand Up @@ -1004,9 +1009,6 @@ impl BorrowedAccount<'_> {
// buffer with MAX_PERMITTED_DATA_INCREASE capacity so that if the
// transaction reallocs, we don't have to copy the whole account data a
// second time to fullfill the realloc.
//
// NOTE: The account memory region CoW code in bpf_loader::create_vm() implements the same
// logic and must be kept in sync.
if self.account.is_shared() {
self.account.reserve(MAX_PERMITTED_DATA_INCREASE);
}
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