江苏龙网

  1. 首页 > 人文 > >

彩色科技|linux内核写时复制机制源代码解读( 三 )

2252行 关联一个anon_vma实例到vma
2255行 到 2259行 判断原来的页表项映射的页是0页 ， 就分配高端可移动的页并用0初始化
2261到2265行 如果不是0页 ， 分配高端可移动的页 ， 然后将原来的页拷贝到新页
2268if (mem_cgroup_try_charge_delay(new_page, mm, GFP_KERNEL,22702271__SetPageUptodate(new_page);22722273mmu_notifier_range_init(2275mmu_notifier_invalidate_range_start(22762277/*2278|* Re-check the pte - we dropped the lock2279|*/2280vmf->pte = pte_offset_map_lock(mm, vmf->pmd, vmf->address,2281if (likely(pte_same(*vmf->pte, vmf->orig_pte))) {2282if (old_page) {2283if (!PageAnon(old_page)) {2284dec_mm_counter_fast(mm,2285mm_counter_file(old_page));2286inc_mm_counter_fast(mm, MM_ANONPAGES);2287}2288} else {2289inc_mm_counter_fast(mm, MM_ANONPAGES);2290}2291flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));2292entry = mk_pte(new_page, vma->vm_page_prot);2293entry = maybe_mkwrite(pte_mkdirty(entry), vma);2294/*2295|* Clear the pte entry and flush it first, before updating the2296|* pte with the new entry. This will avoid a race condition2297|* seen in the presence of one thread doing SMC and another2298|* thread doing COW.2299|*/2300ptep_clear_flush_notify(vma, vmf->address, vmf->pte);2301page_add_new_anon_rmap(new_page, vma, vmf->address, false);2302mem_cgroup_commit_charge(new_page, memcg, false, false);2303lru_cache_add_active_or_unevictable(new_page, vma);2304/*2305|* We call the notify macro here because, when using secondary2306|* mmu page tables (such as kvm shadow page tables), we want the2307|* new page to be mapped directly into the secondary page table.2308|*/2309set_pte_at_notify(mm, vmf->address, vmf->pte, entry);2310update_mmu_cache(vma, vmf->address, vmf->pte);2311if (old_page) {2312/*2313|* Only after switching the pte to the new page may2314|* we remove the mapcount here. Otherwise another2315|* process may come and find the rmap count decremented2316|* before the pte is switched to the new page, and2317|* "reuse" the old page writing into it while our pte2318|* here still points into it and can be read by other2319|* threads.2320|*2321|* The critical issue is to order this2322|* page_remove_rmap with the ptp_clear_flush above.2323|* Those stores are ordered by (if nothing else,)2324|* the barrier present in the atomic_add_negative2325|* in page_remove_rmap.2326|*2327|* Then the TLB flush in ptep_clear_flush ensures that2328|* no process can access the old page before the2329|* decremented mapcount is visible. And the old page2330|* cannot be reused until after the decremented2331|* mapcount is visible. So transitively, TLBs to2332|* old page will be flushed before it can be reused.2333|*/2334page_remove_rmap(old_page, false);2335}23362337/* Free the old page.. */2338new_page = old_page;2339page_copied = 1;2340} else {2341mem_cgroup_cancel_charge(new_page, memcg, false);2342}2271行 设置新的页标识位为PageUptodate ， 表示页中包含有效数据 。
2280行 锁住页表
2281到2339行是发生缺页异常时获得页表项和现在锁住之后获得页表项内容相同的情况
2341 时页表项不同的情况


推荐阅读


上一篇：天下吃货是一家|到底怎么回事？听医生怎么说，让安倍晋三辞职的“溃疡性结肠炎”

下一篇：直面日出|希望尽快结束医疗行业总罢工，文在寅：医生应该守护在患者旁