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Kernel: Support best fit allocation policy in kmalloc()

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Add find_best_fit() which implements best fit allocation algorithm.
Kmalloc now uses a best fit allocation policy for large allocations.
This commit is contained in:
nimelehin 2020-03-10 14:36:20 +03:00 committed by Andreas Kling
parent 0d08ed2693
commit c0a4cf5e8d
Notes: sideshowbarker 2024-07-19 07:52:23 +09:00 
Author: https://github.com/nimelehin
Commit: https://github.com/SerenityOS/serenity/commit/c0a4cf5e8d7
2 changed files with 39 additions and 1 deletions
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29
AK/Bitmap.h
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@ -285,6 +285,35 @@ public:
return {};
}
Optional<size_t> find_best_fit(size_t minimum_length) const
{
size_t start = 0;
size_t best_region_start = 0;
size_t best_region_size = max_size;
bool found = false;
while (true) {
// Look for the next block which is bigger than requested length.
auto length_of_found_range = find_next_range_of_unset_bits(start, minimum_length, best_region_size);
if (length_of_found_range.has_value()) {
if (best_region_size > length_of_found_range.value() || !found) {
best_region_start = start;
best_region_size = length_of_found_range.value();
found = true;
}
start += length_of_found_range.value();
} else {
// There are no ranges which can fit requested length.
break;
}
}
if (found) {
return best_region_start;
}
return {};
}
Bitmap()
: m_size(0)
, m_owned(true)

11
Kernel/Heap/kmalloc.cpp
View file

@ -150,7 +150,16 @@ void* kmalloc_impl(size_t size)
size_t chunks_needed = (real_size + CHUNK_SIZE - 1) / CHUNK_SIZE;
Bitmap bitmap_wrapper = Bitmap::wrap(alloc_map, POOL_SIZE / CHUNK_SIZE);
auto first_chunk = bitmap_wrapper.find_first_fit(chunks_needed);
Optional<size_t> first_chunk;
// Choose the right politic for allocation.
constexpr u32 best_fit_threshold = 128;
if (chunks_needed < best_fit_threshold) {
first_chunk = bitmap_wrapper.find_first_fit(chunks_needed);
} else {
first_chunk = bitmap_wrapper.find_best_fit(chunks_needed);
}
if (!first_chunk.has_value()) {
klog() << "kmalloc(): PANIC! Out of memory (no suitable block for size " << size << ")";
Kernel::dump_backtrace();