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How is cache used in the Linux kernel?
It aims to improve performance of a block device (eg, a spindle) by dynamically migrating some of its data to a faster, smaller device (eg, an SSD). This device-mapper solution allows us to insert this caching at different levels of the dm stack, for instance above the data device for a thin-provisioning pool.
How is the memory mapped to the kernel?
Almost all memory that is directly accessed by the kernel is reached via addresses in the directly mapped range. That range is a large chunk of address space that is mapped to physical memory in a simple, linear fashion, so that, for all practical purposes, it looks as if the kernel is working with physical memory addresses.
How big is the stack in the kernel?
Each process has its own stack for use when it is running in the kernel; in current kernels, that stack is sized at either 8KB or (on 64-bit systems) 16KB of memory. The stack lives in directly-mapped kernel memory, so it must be physically contiguous.
What happens to the metadata of a cache block?
If power is lost you may lose some recent writes. The metadata should always be consistent in spite of any crash. The ‘dirty’ state for a cache block changes far too frequently for us to keep updating it on the fly. So we treat it as a hint.
How often is metadata committed to the cache?
On-disk metadata is committed every time a FLUSH or FUA bio is written. If no such requests are made then commits will occur every second. This means the cache behaves like a physical disk that has a volatile write cache. If power is lost you may lose some recent writes. The metadata should always be consistent in spite of any crash.
What does the constructor of cache do in Linux?
Constructor ¶ metadata dev fast device holding the persistent metad cache dev fast device holding cached data blocks origin dev slow device holding original data blocks block size cache unit size in sectors #feature args number of feature arguments passed
Can you use NTFS as a write cache in Linux?
Firstly, I DO NOT recommend you continue using NTFS, as ntfs implemention in Linux would be performance and security trouble at any time. This will use up to 100% of your free memory as write cache. Or you can go all out and use tmpfs. This is only relevant if you have RAM enough. Put this in /etc/fstab.