/////////////////////////////////////
// PRIVATE METHODS
/////////////////////////////////////
//
// Finds a contiguous block of virtual memory.
//
// *** CALLER MUST HOLD OUR PROTECTIVE LOCK! ***
//
// We don't acquire the spinlock ourselves in case the caller
// wants to do more work within it.
//
// Currently, the approach is VERY simplistic; we just keep handing out
// pages starting with the base of the virtual memory space until we
// bump into the top, and then we become much more inefficient.
//
// The expectation is that higher-level components will do smarter
// space management than this!
//
private unsafe UIntPtr ReserveInternal(UIntPtr numPages, Process process, uint extra, PageType type)
{
DebugStub.Assert(numPages >= 1);
UIntPtr mapAddr = UIntPtr.Zero;
uint tag =
(process != null ? process.ProcessTag : MemoryManager.KernelPage)
| (extra & MemoryManager.ExtraMask)
| (uint)type;
UIntPtr blockBytes = MemoryManager.BytesFromPages(numPages);
if (nextAlloc + blockBytes <= rangeLimit)
{
mapAddr = nextAlloc;
UIntPtr limitAddr = mapAddr + blockBytes;
nextAlloc = limitAddr;
SetRange(mapAddr, limitAddr, tag);
}
else
{
// slow-path allocation - just do first-fit for now...
// TODO: Need to integrate freelist management from flatpages et al
UIntPtr startIdx = PageFromAddr(dataStart);
UIntPtr limitIdx = MemoryManager.PageFromAddr(rangeLimit - descrBase) - (numPages - 1);
DebugStub.Assert(limitIdx <= PageCount);
for (UIntPtr pageIdx = startIdx; pageIdx < limitIdx; pageIdx++)
{
UIntPtr pageCount = 0;
while (pageCount < numPages)
{
uint pageTag = *(pageTable + pageIdx + pageCount);
if (pageTag != MemoryManager.PageFree)
{
break;
}
pageCount++;
}
if (pageCount == numPages)
{
mapAddr = dataStart + MemoryManager.BytesFromPages(pageIdx - startIdx);
SetRange(mapAddr, mapAddr + blockBytes, tag);
break;
}
else
{
pageIdx += pageCount;
}
}
}
return(mapAddr);
}
internal unsafe void SetRange(UIntPtr startAddr, UIntPtr limitAddr, uint tag)
{
DebugStub.Assert(startAddr >= descrBase);
DebugStub.Assert(limitAddr <= descrLimit);
UIntPtr startIdx = PageFromAddr(startAddr);
UIntPtr limitIdx = MemoryManager.PageFromAddr(limitAddr - descrBase);
DebugStub.Assert(limitIdx <= PageCount);
for (UIntPtr i = startIdx; i < limitIdx; i++)
{
pageTable[(uint)i] = tag;
}
}
internal UIntPtr PageFromAddr(UIntPtr addr)
{
DebugStub.Assert(addr >= descrBase);
DebugStub.Assert(addr < descrLimit);
return(MemoryManager.PageFromAddr(addr - descrBase));
}