水平有限,描述不當之處還請指出,轉載請註明出處http://blog.csdn.net/vanbreaker/article/details/7705792
slob釋放對象由函數slob_free()來完成,分爲三種情況進行處理:
- slob中已有的空閒單元加上釋放對象塊的空閒單元正好等於一個空閒的page,那麼將直接將該page釋放回夥伴系統
- slob中已無空閒單元,那麼這次釋放將更新slob的信息
- 普通情況,即slob處於部分滿狀態,那麼更新slob的信息的同時還要將釋放的塊插入到相應的位置,要注意插入後是否能和相鄰塊進行合併!
下面來看具體的代碼
/*
* slob_free: entry point into the slob allocator.
*/
static void slob_free(void *block, int size)
{
struct slob_page *sp;
slob_t *prev, *next, *b = (slob_t *)block;
slobidx_t units;
unsigned long flags;
if (unlikely(ZERO_OR_NULL_PTR(block)))
return;
BUG_ON(!size);
sp = slob_page(block);//獲取slob地址
units = SLOB_UNITS(size);//計算釋放的單元數
spin_lock_irqsave(&slob_lock, flags);
/*slob剩餘的單元數加上待釋放的單元數正好等於一個slob本有的總單元數,
直接將slob佔用的頁框釋放回夥伴系統*/
if (sp->units + units == SLOB_UNITS(PAGE_SIZE)) {
/* Go directly to page allocator. Do not pass slob allocator */
if (slob_page_free(sp))
clear_slob_page_free(sp);
spin_unlock_irqrestore(&slob_lock, flags);
clear_slob_page(sp);
free_slob_page(sp);
slob_free_pages(b, 0);
return;
}
if (!slob_page_free(sp)) {//slob沒有空閒塊
/* This slob page is about to become partially free. Easy! */
sp->units = units;//設置slob的單元數爲釋放對象的單元數
sp->free = b;//設置首對象爲釋放對象
set_slob(b, units,//最後一個對象的空閒對象設置爲下一個頁的首個單元
(void *)((unsigned long)(b +
SLOB_UNITS(PAGE_SIZE)) & PAGE_MASK));
set_slob_page_free(sp, &free_slob_small);//將slob鏈入free_slob_small鏈表
goto out;
}
/*
* Otherwise the page is already partially free, so find reinsertion
* point.
*/
sp->units += units;//空閒單元總數增加units
if (b < sp->free) {//待釋放塊的地址小於sp->free
if (b + units == sp->free) {//可以合併
units += slob_units(sp->free);
sp->free = slob_next(sp->free);//取free的下一個空閒對象作爲free
}
/*將釋放塊插入在free前面,並將其作爲首個空閒塊賦給free*/
set_slob(b, units, sp->free);
sp->free = b;
} else {
prev = sp->free;//取首個空閒塊
next = slob_next(prev);//取第二個空閒塊
while (b > next) {//掃描至待釋放塊處
prev = next;
next = slob_next(prev);
}
/*將b插在prev和next中間,prev-->b-->next,要考慮是否能夠合併*/
/*如果prev不是最後一個空閒塊並且b可以和next合併,則進行合併*/
if (!slob_last(prev) && b + units == next) {
units += slob_units(next);
set_slob(b, units, slob_next(next));
} else//否則將b插入在next前面
set_slob(b, units, next);
if (prev + slob_units(prev) == b) {//如果prev可以和b合併,則進行合併
units = slob_units(b) + slob_units(prev);
set_slob(prev, units, slob_next(b));
} else//否則,將b插在prev後面
set_slob(prev, slob_units(prev), b);
}
out:
spin_unlock_irqrestore(&slob_lock, flags);
}