When a file is created by a process, its owner ID is the UID of the process. Its owner user group ID can be either the process group ID of the creator process or the user group ID of the parent directory, depending on the value of the sgid flag of the par- ent directory. (查看原文)
Three Thread-Local Storage (TLS) segments: this is a mechanism that allows multithreaded applications to make use of up to three segments containing data local to each thread. The set_thread_area() and get_thread_area() system calls, respectively, create and release a TLS segment for the executing process. (查看原文)
Besides general-purpose hardware caches, 80 × 86 processors include another cache called Translation Lookaside Buffers (TLB) to speed up linear address translation. When a linear address is used for the first time, the corresponding physical address is computed through slow accesses to the Page Tables in RAM. The physical address is then stored in a TLB entry so that further references to the same linear address can be quickly translated.
In a multiprocessor system, each CPU has its own TLB, called the local TLB of the CPU. Contrary to the hardware cache, the corresponding entries of the TLB need not be synchronized, because processes running on the existing CPUs may associate the same linear address with different physical ones.
When the cr3 control register of a CPU is modified, the ha... (查看原文)
As a general rule, any process switch implies changing the set of active page tables. Local TLB entries relative to the old page tables must be flushed; this is done auto- matically when the kernel writes the address of the new Page Global Directory into the cr3 control register. The kernel succeeds, however, in avoiding TLB flushes in the following cases:
• When performing a process switch between two regular processes that use the same set of page tables (see the section “The schedule() Function” in Chapter 7).
• When performing a process switch between a regular process and a kernel thread. In fact, we’ll see in the section “Memory Descriptor of Kernel Threads” in Chapter 9, that kernel threads do not have their own set of page tables; rather, they use the set of page tables ow... (查看原文)
From the kernel's point of view, the purpose of a process is to act as an entity to which system
resources (CPU time, memory, etc.) are allocated.
The Unix operating system design is centered on its filesystem, A Unix
file is an information container structured as a sequence of bytes.
A filename included in a directory is called a file hard link, or more
simply, a link.
Unix makes a clear distinction between the contents of a file and the
information about a file(inode).
Because a process in User Mode cannot directly interact with the
low-level hardware components, each actual file operation must be
performed in Kernel Mode. Therefore, the Unix operating system defines
several system calls related to file handling.
All Unix kernels are reentrant. One way to provide reentrancy is to... (查看原文)
From the kernel's point of view, the *purpose* of a process is to act as an entity to which system resources(CPU time, memory, etc) are allocated. (查看原文)
a noncontiguous memory area can be allocated by the vmalloc_32( ) function, which is very similar to vmalloc( ) but only allocates page frames from the ZONE_NORMAL and ZONE_DMA memory zones. (查看原文)
