Maximum number of pending "background" requests. A
background request is any type of request for which the
total number is not limited by other means. As of kernel
4.8, only two types of requests fall into this category:
1. Read-ahead requests
2. Asynchronous direct I/O requests
Read-ahead requests are generated (if max_readahead is
non-zero) by the kernel to preemptively fill its caches
when it anticipates that userspace will soon read more
data.
Asynchronous direct I/O requests are generated if
FUSE_CAP_ASYNC_DIO is enabled and userspace submits a large
direct I/O request. In this case the kernel will internally
split it up into multiple smaller requests and submit them
to the filesystem concurrently.
Note that the following requests are *not* background
requests: writeback requests (limited by the kernel's
flusher algorithm), regular (i.e., synchronous and
buffered) userspace read/write requests (limited to one per
thread), asynchronous read requests (Linux's io_submit(2)
call actually blocks, so these are also limited to one per
thread).
Maximum number of pending "background" requests. A background request is any type of request for which the total number is not limited by other means. As of kernel 4.8, only two types of requests fall into this category:
1. Read-ahead requests 2. Asynchronous direct I/O requests
Read-ahead requests are generated (if max_readahead is non-zero) by the kernel to preemptively fill its caches when it anticipates that userspace will soon read more data.
Asynchronous direct I/O requests are generated if FUSE_CAP_ASYNC_DIO is enabled and userspace submits a large direct I/O request. In this case the kernel will internally split it up into multiple smaller requests and submit them to the filesystem concurrently.
Note that the following requests are *not* background requests: writeback requests (limited by the kernel's flusher algorithm), regular (i.e., synchronous and buffered) userspace read/write requests (limited to one per thread), asynchronous read requests (Linux's io_submit(2) call actually blocks, so these are also limited to one per thread).