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kernel/vm: Ignore insertion hints when the address space is over half full.

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We ideally want to avoid further fragmentation and just insert in the
smallest possible slot in that case.

Part of #19592. With DISABLE_ASLR=1, seems to save about 120 MB or so
of address space, which is a lot on 32-bit.
This commit is contained in:
Augustin Cavalier
2025-07-01 00:22:32 -04:00
parent da5a0edd02
commit e16d28419f
1 changed files with 5 additions and 4 deletions
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src/system/kernel/vm/VMUserAddressSpace.cpp
+5 -4
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@@ -578,15 +578,16 @@ VMUserAddressSpace::_InsertAreaSlot(addr_t start, addr_t size, addr_t end,
start = align_address(start, alignment);
bool useHint
= addressSpec != B_EXACT_ADDRESS && !is_base_address_spec(addressSpec);
bool useHint = addressSpec != B_EXACT_ADDRESS
&& !is_base_address_spec(addressSpec)
&& fFreeSpace > (Size() / 2);
addr_t originalStart = 0;
if (fRandomizingEnabled && addressSpec == B_RANDOMIZED_BASE_ADDRESS) {
originalStart = start;
start = _RandomizeAddress(start, end - size + 1, alignment, true);
} else if (useHint
&& start <= fNextInsertHint && fNextInsertHint <= end - size + 1) {
&& start <= fNextInsertHint && fNextInsertHint <= (end - size + 1)) {
originalStart = start;
start = fNextInsertHint;
}
@@ -595,7 +596,7 @@ VMUserAddressSpace::_InsertAreaSlot(addr_t start, addr_t size, addr_t end,
second_chance:
VMUserArea* next = fAreas.FindClosest(start + size, false);
VMUserArea* last = next != NULL
? fAreas.Previous(next) : fAreas.FindClosest(start + size, true);
? fAreas.Previous(next) : fAreas.FindClosest(start + size, true);
// find the right spot depending on the address specification - the area
// will be inserted directly after "last" ("next" is not referenced anymore)