/* translate virtual address to pysical address. handles tlbmiss, page faults,
loads page to physical memory in case of page fault */
int translate(VirtualAddress address, PhysicalAddress &physicalAddress)
{
int rval = status_success;
PageEntry pageEntry; /* the page entry from page table. We use this for lookup in page table, and get frame no from it */
Page page; /* in case we need to get page from backing store and add it to physical memory */
FrameNumber frameno; /* in case we need to add page to physical memory */
PageNumber pageno = -1; /* page number we will lookkup. get this from virtual address */
int offset = -1; /* offset we will lookkup. get this from virtual address */
bool pagehit = false; /* flags */
bool tlbhit = false;
/* break address to page no offset */
zlog(ZLOG_LOC, "VirtualMemoryManager::translate- get page number and offset\n");
pageno = getPageNumberFromLogicalAddress(address);
offset = getOffsetFromLogicalAddress(address);
/* we are storing he required frame number in the frameno value, weather we get a hit
from tlb, page table or page fault */
/* check in tlb */
tlb.lookup(pageno, frameno, tlbhit);
if(true == tlbhit)
{
/* we are done here */
zlog(ZLOG_LOC, "VirtualMemoryManager::translate - tlbhit !!\n");
tlbhits++;
}
else
{
/* check in page table tlb miss */
zlog(ZLOG_LOC, "VirtualMemoryManager::translate- get page entry for page no : %d\n", pageno);
if(status_success != pageTable.lookup(pageno, pageEntry))
{
rval = status_failure;
zlog(ZLOG_LOC, "VirtualMemoryManager::translate- unable to get page table entry\n");
goto exit1;
}
/* check if this is a page fault */
zlog(ZLOG_LOC, "VirtualMemoryManager::translate- check for page fault\n");
if(true == pageEntry.isValid)
{
/* we are done */
zlog(ZLOG_LOC, "VirtualMemoryManager::translate- page hit! \n");
frameno = pageEntry.frameNumber;
pagehit = true;
/* update counter */
pagehits++;
}
/* page fault code */
if(false == pagehit)
{
/* update counter */
pagefaults++;
/* get page from backing store */
zlog(ZLOG_LOC, "VirtualMemoryManager::translate- page fault on page : %d, reading block : %d from backing store\n",
pageno, pageno);
if(status_success != backingStore.getPage(page, pageno*PageSize, PageSize))
{
zlog(ZLOG_LOC, "VirtualMemoryManager::translate- unable to get page form backing store\n");
rval = status_failure;
goto exit2;
}
/* add to physical memory */
zlog(ZLOG_LOC, "VirtualMemoryManager::translate- putting the page in physical memory\n");
if(status_success != physicalMemory.addPage(page, frameno))
{
zlog(ZLOG_LOC, "VirtualMemoryManager::translate- unable to add page to physical memory\n");
rval = status_failure;
goto exit2;
}
/* update page entry */
zlog(ZLOG_LOC, "VirtualMemoryManager::translate- update page Entry \n");
pageEntry.frameNumber = frameno;
pageEntry.isModified = false;
pageEntry.isValid = true;
/* add page entry to page table */
zlog(ZLOG_LOC, "VirtualMemoryManager::translate- update page table\n");
if(status_success != pageTable.updatePageEntry(pageEntry, pageno))
{
zlog(ZLOG_LOC, "VirtualMemoryManager::translate- unable to add entry to page table\n");
rval = status_failure;
goto exit2;
}
zlog(ZLOG_LOC, "VirtualMemoryManager::translate- lookup page table again\n");
frameno = pageEntry.frameNumber;
pagehit = true;
}
/* by this time we have a valid page frame mapping
if there was a tlb miss, update tlb table */
if(false == tlbhit)
{
TlbEntry tlbEntry;
tlbEntry.pageNumber = pageno;
tlbEntry.frameNumber = frameno;
tlbEntry.valid = true;
tlb.addEntry(tlbEntry);
}
}
/* page entry contains the frame number required */
physicalAddress = (frameno << numBitsForFrameOffset) + offset;
exit2:
exit1:
return rval;
}
