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Remove at_least

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The Pal was providing policy for overallocating a block of memory to
achieve alignment make that part of the backend.
The backend should be responsible for layout policy.
This commit is contained in:
Matthew Parkinson
2021-07-19 11:20:02 +01:00
committed by Matthew Parkinson
parent 9df0101dfd
commit 5d0ae71423
10 changed files with 50 additions and 68 deletions
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21
src/backend/address_space.h
View File

@@ -96,12 +96,21 @@ namespace snmalloc
else if constexpr (!pal_supports<NoAllocation, PAL>)
{
// Need at least 2 times the space to guarantee alignment.
// Hold lock here as a race could cause additional requests to
// the PAL, and this could lead to suprious OOM. This is
// particularly bad if the PAL gives all the memory on first call.
auto block_and_size = PAL::reserve_at_least(size * 2);
block = CapPtr<void, CBChunk>(block_and_size.first);
block_size = block_and_size.second;
size_t needed_size = size * 2;
// Magic number (27) for over-allocating a block of memory
// These should be further refined based on experiments.
constexpr size_t min_size = bits::one_at_bit(27);
for (size_t size_request = bits::max(needed_size, min_size);
size_request >= needed_size;
size_request = size_request / 2)
{
block = CapPtr<void, CBChunk>(PAL::reserve(size_request));
if (block != nullptr)
{
block_size = size_request;
break;
}
}
// Ensure block is pointer aligned.
if (

2
src/backend/backend.h
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@@ -11,7 +11,7 @@ namespace snmalloc
* This class implements the standard backend for handling allocations.
* It abstracts page table management and address space management.
*/
template<typename PAL, bool fixed_range>
template<SNMALLOC_CONCEPT(ConceptPAL) PAL, bool fixed_range>
class BackendAllocator
{
public:

4
src/backend/pagemap.h
View File

@@ -119,9 +119,7 @@ namespace snmalloc
// TODO request additional space, and move to random offset.
// TODO wasting space if size2 bigger than needed.
auto [new_body_untyped, size2] =
Pal::reserve_at_least(ENTRIES * sizeof(T));
auto new_body_untyped = Pal::reserve(ENTRIES * sizeof(T));
auto new_body = reinterpret_cast<T*>(new_body_untyped);

16
src/pal/pal_concept.h
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@@ -52,11 +52,10 @@ namespace snmalloc
* Absent any feature flags, the PAL must support a crude primitive allocator
*/
template<typename PAL>
concept ConceptPAL_reserve_at_least =
requires(PAL p, void* vp, std::size_t sz)
concept ConceptPAL_reserve =
requires(PAL p, std::size_t sz)
{
{ PAL::reserve_at_least(sz) } noexcept
-> ConceptSame<std::pair<void*, std::size_t>>;
{ PAL::reserve(sz) } noexcept -> ConceptSame<void*>;
};
/**
@@ -102,10 +101,11 @@ namespace snmalloc
(!pal_supports<LowMemoryNotification, PAL> ||
ConceptPAL_mem_low_notify<PAL>) &&
(pal_supports<NoAllocation, PAL> ||
(pal_supports<AlignedAllocation, PAL> &&
ConceptPAL_reserve_aligned<PAL>) ||
(!pal_supports<AlignedAllocation, PAL> &&
ConceptPAL_reserve_at_least<PAL>));
(
(!pal_supports<AlignedAllocation, PAL> ||
ConceptPAL_reserve_aligned<PAL>) &&
ConceptPAL_reserve<PAL>)
);
} // namespace snmalloc
#endif

40
src/pal/pal_posix.h
View File

@@ -253,44 +253,32 @@ namespace snmalloc
* POSIX does not define a portable interface for specifying alignment
* greater than a page.
*/
static std::pair<void*, size_t> reserve_at_least(size_t size) noexcept
static void* reserve(size_t size) noexcept
{
SNMALLOC_ASSERT(bits::is_pow2(size));
// Magic number for over-allocating chosen by the Pal
// These should be further refined based on experiments.
constexpr size_t min_size =
bits::is64() ? bits::one_at_bit(31) : bits::one_at_bit(27);
#ifdef SNMALLOC_CHECK_CLIENT
auto prot = PROT_NONE;
#else
auto prot = PROT_READ | PROT_WRITE;
#endif
for (size_t size_request = bits::max(size, min_size);
size_request >= size;
size_request = size_request / 2)
{
void* p = mmap(
nullptr,
size_request,
prot,
MAP_PRIVATE | MAP_ANONYMOUS | DefaultMMAPFlags<OS>::flags,
AnonFD<OS>::fd,
0);
void* p = mmap(
nullptr,
size,
prot,
MAP_PRIVATE | MAP_ANONYMOUS | DefaultMMAPFlags<OS>::flags,
AnonFD<OS>::fd,
0);
if (p != MAP_FAILED)
{
if (p != MAP_FAILED)
{
#ifdef SNMALLOC_TRACING
std::cout << "Pal_posix reserved: " << p << " (" << size_request
<< ")" << std::endl;
std::cout << "Pal_posix reserved: " << p << " (" << size << ")"
<< std::endl;
#endif
return {p, size_request};
}
return p;
}
OS::error("Out of memory");
return nullptr;
}
/**

21
src/pal/pal_windows.h
View File

@@ -185,26 +185,9 @@ namespace snmalloc
}
# endif
static std::pair<void*, size_t> reserve_at_least(size_t size) noexcept
static void* reserve(size_t size) noexcept
{
SNMALLOC_ASSERT(bits::is_pow2(size));
// Magic number for over-allocating chosen by the Pal
// These should be further refined based on experiments.
constexpr size_t min_size =
bits::is64() ? bits::one_at_bit(32) : bits::one_at_bit(28);
for (size_t size_request = bits::max(size, min_size);
size_request >= size;
size_request = size_request / 2)
{
void* ret =
VirtualAlloc(nullptr, size_request, MEM_RESERVE, PAGE_READWRITE);
if (ret != nullptr)
{
return std::pair(ret, size_request);
}
}
error("Failed to allocate memory\n");
return VirtualAlloc(nullptr, size, MEM_RESERVE, PAGE_READWRITE);
}
/**

3
src/test/func/fixed_region/fixed_region.cc
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@@ -21,7 +21,8 @@ int main()
// 28 is large enough to produce a nested allocator.
// It is also large enough for the example to run in.
// For 1MiB superslabs, SUPERSLAB_BITS + 4 is not big enough for the example.
auto [oe_base, size] = Pal::reserve_at_least(bits::one_at_bit(28));
auto size = bits::one_at_bit(28);
auto oe_base = Pal::reserve(size);
Pal::notify_using<NoZero>(oe_base, size);
auto oe_end = pointer_offset(oe_base, size);
std::cout << "Allocated region " << oe_base << " - "

3
src/test/func/pagemap/pagemap.cc
View File

@@ -68,7 +68,8 @@ void test_pagemap(bool bounded)
// Initialise the pagemap
if (bounded)
{
auto [base, size] = Pal::reserve_at_least(bits::one_at_bit(30));
auto size = bits::one_at_bit(30);
auto base = Pal::reserve(size);
Pal::notify_using<NoZero>(base, size);
std::cout << "Fixed base: " << base << " (" << size << ") "
<< " end: " << pointer_offset(base, size) << std::endl;

2
src/test/perf/external_pointer/externalpointer.cc
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@@ -32,6 +32,8 @@ namespace test
size = 16;
// store object
objects[i] = (size_t*)alloc.alloc(size);
if (objects[i] == nullptr)
abort();
// Store allocators size for this object
*objects[i] = alloc.alloc_size(objects[i]);
}