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vm_page_allocate_page_run: use a mask to enforce the boundary

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* use a mask to enforce the boundary as suggested by Ingo. Thanks!
This commit is contained in:
Jerome Duval
2012-11-09 00:21:41 +01:00
parent d3f77ddee3
commit 5ad12a800d
1 changed files with 8 additions and 11 deletions
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src/system/kernel/vm/vm_page.cpp
+8 -11
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@@ -3831,8 +3831,8 @@ vm_page_allocate_page_run(uint32 flags, page_num_t length,
ASSERT(((alignmentMask + 1) & alignmentMask) == 0); ASSERT(((alignmentMask + 1) & alignmentMask) == 0);
// alignment must be a power of 2 // alignment must be a power of 2
// compute the boundary shift // compute the boundary mask
uint32 boundaryShift = 0; uint32 boundaryMask = 0;
if (restrictions->boundary != 0) { if (restrictions->boundary != 0) {
page_num_t boundary = restrictions->boundary / B_PAGE_SIZE; page_num_t boundary = restrictions->boundary / B_PAGE_SIZE;
// boundary must be a power of two and not less than alignment and // boundary must be a power of two and not less than alignment and
@@ -3841,8 +3841,7 @@ vm_page_allocate_page_run(uint32 flags, page_num_t length,
ASSERT(boundary >= alignmentMask + 1); ASSERT(boundary >= alignmentMask + 1);
ASSERT(boundary >= length); ASSERT(boundary >= length);
while ((boundary >>= 1) > 0) boundaryMask = -boundary;
boundaryShift++;
} }
vm_page_reservation reservation; vm_page_reservation reservation;
@@ -3858,19 +3857,17 @@ vm_page_allocate_page_run(uint32 flags, page_num_t length,
int useCached = freePages > 0 && (page_num_t)freePages > 2 * length ? 0 : 1; int useCached = freePages > 0 && (page_num_t)freePages > 2 * length ? 0 : 1;
for (;;) { for (;;) {
if (alignmentMask != 0 || boundaryShift != 0) { if (alignmentMask != 0 || boundaryMask != 0) {
page_num_t offsetStart = start + sPhysicalPageOffset; page_num_t offsetStart = start + sPhysicalPageOffset;
// enforce alignment // enforce alignment
if ((offsetStart & alignmentMask) != 0) { if ((offsetStart & alignmentMask) != 0)
offsetStart = (offsetStart + alignmentMask) & ~alignmentMask; offsetStart = (offsetStart + alignmentMask) & ~alignmentMask;
}
// enforce boundary // enforce boundary
if (boundaryShift != 0 && offsetStart << boundaryShift if (boundaryMask != 0 && ((offsetStart ^ (offsetStart
!= (offsetStart + length - 1) << boundaryShift) { + length - 1)) & boundaryMask) != 0) {
offsetStart = (offsetStart + length - 1) << boundaryShift offsetStart = (offsetStart + length - 1) & boundaryMask;
>> boundaryShift;
} }
start = offsetStart - sPhysicalPageOffset; start = offsetStart - sPhysicalPageOffset;