What is Linux cache?
The cache in linux is called the Page Cache. This means if data is written to disk it is written to memory into the cache and marked as dirty in the cache until it is synchronized to disk. The kernel maintains internal data structures to optimize which data to evict from cache when more space is needed in the cache.
Are buffer and cache the same?
Cache is a high-speed storage area while a buffer is a normal storage area on ram for temporary storage. 2. Cache is made from static ram which is faster than the slower dynamic ram used for a buffer. Cache can also be a section of the disk while a buffer is only a section of the ram.
Why do we use a cache in Linux?
Typically Linux uses a cache to asynchronously write the data to the disk. However, it may happen that the time span between the write request and the actual write or the amount of unwritten (dirty) data becomes very large.
What happens when I write a large file in Linux?
So on my Linux desktop, I’m writing some large file either to a local disk or an NFS mount. There is some kind of system buffer that the to-be-written data is cached in. (Something in the range of 0.5-2GB on my system, I think?) If the buffer is full, all file access blocks, effectively freezing the system until the write is done.
What to do if VFS cache pressure is too high?
Increasing vfs_cache_pressure may help but the only real fix is to get more RAM. Having vfs_cache_pressure set to high number sacrifices average performance for having more stable performance overall (that is, you can avoid really bad worst case behavior but have to deal with worse overall performance).
How to configure filesystems in Linux system?
Worth noting for the HDD case is high fifo_expire_async (usually write) and long slice_sync to allow a single process to get high throughput (set slice_sync to lower number if you hit situations where multiple processes are waiting for some data from the disk in parallel).