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Changes PMM internals from "all free" to "all used". Adds markFree, removes markOccupied.

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This commit is contained in:
Felix Queißner 2016-05-04 17:33:53 +02:00
parent 15cabe92ad
commit 87f83eeca3
2 changed files with 11 additions and 13 deletions
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5
prototypes/base/include/pmm.hpp
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@ -11,10 +11,9 @@ private:
PMM() = delete;
public:
/**
* Marks a page as occupied by external memory management.
* @returns true if the page was previously free, false if it was already allocated.
* Marks a page as free by external memory management.
*/
static bool markOccupied(physical_t page);
static void markFree(physical_t page);
/**
* Allocates a single page.

19
prototypes/base/src/pmm.cpp
View file

@ -14,8 +14,8 @@ static const uint32_t BitmapLength = BitmapSize / 32;
/**
* Bitmap that stores the page status.
* A set bit marks a used page
* An unset bit marks an unused page
* A set bit marks a page as free.
* An unset bit marks a page as used.
*/
static uint32_t bitmap[BitmapLength];
@ -27,7 +27,7 @@ static bool isAligned(uint32_t ptr)
return (ptr % 4096) == 0;
}
bool PMM::markOccupied(physical_t page)
void PMM::markFree(physical_t page)
{
uint32_t ptr = page.numeric();
if(!isAligned(ptr))
@ -37,26 +37,25 @@ bool PMM::markOccupied(physical_t page)
uint32_t idx = pageId / 32;
uint32_t bit = pageId % 32;
bool wasSet = (bitmap[idx] & (1<<bit)) != 0;
bitmap[idx] |= (1<<bit);
return wasSet;
}
physical_t PMM::alloc(bool &success)
{
for(uint32_t idx = 0; idx < BitmapLength; idx++) {
// fast skip when all bits are set
if(bitmap[idx] == 0xFFFFFFFF) {
// fast skip when no bit is set
if(bitmap[idx] == 0) {
continue;
}
for(uint32_t bit = 0; bit < 32; bit++) {
uint32_t mask = (1<<bit);
if((bitmap[idx] & mask) != 0) {
if((bitmap[idx] & mask) == 0) {
// If bit is not set, ignore the bit.
continue;
}
// Mark the selected bit as used.
bitmap[idx] |= mask;
bitmap[idx] &= ~mask;
uint32_t pageId = 32 * idx + bit;
uint32_t ptr = 4096 * pageId;
@ -82,5 +81,5 @@ void PMM::free(physical_t page)
uint32_t bit = pageId % 32;
// Mark the selected bit as free.
bitmap[idx] &= ~(1<<bit);
bitmap[idx] |= (1<<bit);
}