Brian Fundakowski Feldman wrote:
On Mon, Dec 26, 2005 at 01:47:20PM +0000, Diomidis Spinellis wrote:
dds 2005-12-26 13:47:20 UTC
FreeBSD src repository
Modified files: (Branch: RELENG_6)
sys/kern kern_exec.c vfs_subr.c
sys/sys vnode.h
sys/ufs/ufs ufs_vnops.c
sys/vm vm_mmap.c
Log:
MFC changes from 2005.10.26:
Move execve's access time update functionality into a
new vfs_mark_atime() function, and use the new function
for performing efficient atime updates in mmap().
Do you have any particular use cases that are improved a lot by
(seemingly) reducing gratuitous seeks for R/W file mappings?
Substantial improvement for the general case of not-noatime?
I have no comparative tests or use cases, because the base case was an
earlier less-than-perfect change that only lived in HEAD for a week.
The claimed "efficient atime updates in mmap()" are over an earlier
change I committed to HEAD, but never MFCd (vm_mmap.c 1.202). I
introduced that change to fix the behavior where reads through mmap(2)d
files did not update the file's atime. As a result, for example, our
implementation of cp(1) would copy files without updating the atime of
the source. For that earlier change, bde@ complained: "This is a large
pessimization for nfs and a usually-small pessimization for local file
systems." The current implementation fixes that problem by following
the existing approach in execve(2) (the then-named VA_EXECVE_ATIME
flag), and is also cleaner than the earlier one.
Diomidis
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