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PageCache.cpp
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PageCache.cpp
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#include "PageCache.h"
PageCache PageCache::_sInst;
// 向系统申请k页内存
void* PageCache::SystemAllocPage(size_t k)
{
return ::SystemAlloc(k);
}
Span* PageCache::NewSpan(size_t k)
{
std::lock_guard<std::recursive_mutex> lock(_mtx);
// 针对直接申请大于NPAGES的大块内存,直接找系统要
if (k >= NPAGES)
{
void* ptr = SystemAllocPage(k);
Span* span = new Span;
span->_pageId = (ADDRES_INT)ptr >> PAGE_SHIFT;
span->_n = k;
{
//std::lock_guard<std::mutex> lock(_map_mtx);
_idSpanMap[span->_pageId] = span;
}
return span;
}
if (!_spanList[k].Empty()) // 要找的那个页数的span不为空,就直接拿
{
return _spanList[k].PopFront();
}
for (size_t i = k + 1; i < NPAGES; ++i) // 为空就去找比它大的页,切开
{
// 大页给切小,切成k页的span返回
// 切出i-k页挂回自由链表
if (!_spanList[i].Empty())
{
// 1、头切
/*Span* span = _spanList[i].Begin();
_spanList->Erase(span);
Span* splitSpan = new Span;
splitSpan->_pageId = span->_pageId + k;
splitSpan->_n = span->_n - k;
span->_n = k;
_spanList[splitSpan->_n].Insert(_spanList[splitSpan->_n].Begin(), splitSpan);
return span;*/
// 2、或尾切出一个k页span
Span* span = _spanList[i].PopFront();
Span* split = new Span;
split->_pageId = span->_pageId + span->_n - k;
split->_n = k;
// 改变切出来span的页号和span的映射关系
{
//std::lock_guard<std::mutex> lock(_map_mtx);
for (PageID i = 0; i < k; ++i)
{
_idSpanMap[split->_pageId + i] = split;
}
}
span->_n -= k;
_spanList[span->_n].PushFront(span);
return split; // return切出来的那个需要的那个span
}
}
// 所有都没有,申请一个最大的span
Span* bigSpan = new Span;
void* memory = SystemAllocPage(NPAGES - 1);
bigSpan->_pageId = (size_t)memory >> 12;
bigSpan->_n = NPAGES - 1;
{
// 按页号和span映射关系建立
for (PageID i = 0; i < bigSpan->_n; ++i)
{
PageID id = bigSpan->_pageId + i;
_idSpanMap[id] = bigSpan;
}
}
_spanList[NPAGES - 1].Insert(_spanList[NPAGES - 1].Begin(), bigSpan);
return NewSpan(k);
}
Span* PageCache::MapObjectToSpan(void* obj)
{
PageID id = (ADDRES_INT)obj >> PAGE_SHIFT;
/*auto ret = _idSpanMap.find(id);
if (ret != _idSpanMap.end())
{
return ret->second;
}
else
{
assert(false);
return nullptr;
}*/
Span* span = _idSpanMap.get(id);
if (span != nullptr)
{
return span;
}
else
{
assert(false);
return nullptr;
}
}
void PageCache::ReleaseSpanToPageCache(Span* span)
{
if (span->_n >= NPAGES)
{
{
_idSpanMap.erase(span->_pageId);
}
void* ptr = (void*)(span->_pageId << PAGE_SHIFT);
SystemFree(ptr);
delete span;
return;
}
std::lock_guard<std::recursive_mutex> lock(_mtx);
// 检查前后空闲span页,进行合并,解决内存碎片问题
// 向前合并
while (1)
{
PageID preId = span->_pageId - 1;
//auto ret = _idSpanMap.find(preId);
//// 如果前一个页的span不存在,未分配,结束向前合并
//if (ret == _idSpanMap.end())
//{
// break;
//}
Span* preSpan = _idSpanMap.get(preId);// 拿到前一个span
if (preSpan == nullptr)
{
break;
}
// 如果前一个页的span还在使用中,结束向前合并
if (preSpan->_usecount != 0)
{
break;
}
// 开始合并...
// 超过128页,不需要合并了
if (preSpan->_n + span->_n >= NPAGES)
{
break;
}
// 从对应的span链表中解下来,再合并
_spanList[preSpan->_n].Erase(preSpan);
span->_pageId = preSpan->_pageId;
span->_n += preSpan->_n;
// 更新页之间映射关系
{
//std::lock_guard<std::mutex> lock(_map_mtx);
for (PageID i = 0; i < preSpan->_n; ++i)
{
_idSpanMap[preSpan->_pageId + i] = span;
}
}
delete preSpan;
}
// 向后合并
while (1)
{
PageID nextId = span->_pageId + span->_n;
Span* nextSpan = _idSpanMap.get(nextId);
if (nextSpan == nullptr)
{
break;
}
if (nextSpan->_usecount != 0)
{
break;
}
// 超过128页,不需要合并了
if (nextSpan->_n + span->_n >= NPAGES)
{
break;
}
_spanList[nextSpan->_n].Erase(nextSpan);
span->_n += nextSpan->_n;
{
//std::lock_guard<std::mutex> lock(_map_mtx);
for (PageID i = 0; i < nextSpan->_n; ++i)
{
_idSpanMap[nextSpan->_pageId + i] = span;
}
}
delete nextSpan;
}
// 合并出的大span,插入到对应的链表中
_spanList[span->_n].PushFront(span);
}