page fault
2015-10-15
关于 linux 内存管理的一些知识点。下面是缺页的各种情况
/*
* Different kinds of faults, as returned by handle_mm_fault().
* Used to decide whether a process gets delivered SIGBUS or
* just gets major/minor fault counters bumped up.
*/
#define VM_FAULT_MINOR 0 /* For backwards compat. Remove me quickly. */
#define VM_FAULT_OOM 0x0001
#define VM_FAULT_SIGBUS 0x0002
#define VM_FAULT_MAJOR 0x0004
#define VM_FAULT_WRITE 0x0008 /* Special case for get_user_pages */
#define VM_FAULT_HWPOISON 0x0010 /* Hit poisoned small page */
#define VM_FAULT_HWPOISON_LARGE 0x0020 /* Hit poisoned large page. Index encoded in upper bits */
#define VM_FAULT_SIGSEGV 0x0040
#define VM_FAULT_NOPAGE 0x0100 /* ->fault installed the pte, not return page */
#define VM_FAULT_LOCKED 0x0200 /* ->fault locked the returned page */
#define VM_FAULT_RETRY 0x0400 /* ->fault blocked, must retry */
#define VM_FAULT_FALLBACK 0x0800 /* huge page fault failed, fall back to small */
#define VM_FAULT_HWPOISON_LARGE_MASK 0xf000 /* encodes hpage index for large hwpoison */
#define VM_FAULT_ERROR (VM_FAULT_OOM | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | \
VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE | \
VM_FAULT_FALLBACK)
- VM_FAULT_MINOR 表明该页数据已经在内存中了，这种情况不会阻塞进程
- VM_FAULT_MAJOR 表明数据需要从块设备中读取，这种情况会阻塞进程
提供一个 systemtap 脚本
[root@docker221 memory]# pwd
/usr/share/systemtap-2.9-3823/share/doc/systemtap/examples/memory
[root@docker221 memory]# cat pfaults.stp
#! /usr/bin/env stap
global fault_entry_time, fault_address, fault_access
global time_offset
probe begin { time_offset = gettimeofday_us() }
probe vm.pagefault {
t = gettimeofday_us()
fault_entry_time[tid()] = t
fault_address[tid()] = address
fault_access[tid()] = write_access ? "w" : "r"
}
probe vm.pagefault.return {
t=gettimeofday_us()
if (!(tid() in fault_entry_time)) next
e = t - fault_entry_time[id]
if (vm_fault_contains(fault_type,VM_FAULT_MINOR)) {
ftype="minor"
} else if (vm_fault_contains(fault_type,VM_FAULT_MAJOR)) {
ftype="major"
} else {
next #only want to deal with minor and major page faults
}
printf("%d:%d:%id:%s:%s:%d\n",
t - time_offset, tid(), fault_address[tid()], fault_access[tid()], ftype, e)
#free up memory
delete fault_entry_time[tid()]
delete fault_address[tid()]
delete fault_access[tid()]
}
参考
- http://tomoyo.osdn.jp/cgi-bin/lxr/source/include/linux/mm.h#L1028
