KernelTrap: Batched Writes

“Hans Reiser described a recently posted patch as, ‘it revises
the existing reiser4 code to do a good job for writes that are
larger than 4k at a time by assiduously adhering to the principle
that things that need to be done once per write should be done once
per write, not once per 4k.’ He went on to explain, ‘this code
empirically proves that the generic code design which passes 4k at
a time to the underlying FS can be improved. Performance results
show that the new code consumes 40% less CPU when doing ‘dd
bs=1MB…” Referring to generic_file_write(), he further noted
that currently when writing 64MB of data, ‘it may go to the kernel
as a 64MB write, but VFS sends it to the FS as 64MB/4k separate 4k
writes.’ It was acknowledged that this could also be accomplished
in a non-generic way, howevever earlier feedback had suggested that
such improvements should be made available to all…”

Complete Story