Re: [PATCH RFC] vfs: add a O_NOMTIME flag

On Mon 11-05-15 09:24:09, Sage Weil wrote:

On Mon, 11 May 2015, Theodore Ts'o wrote:

quoted

On Sun, May 10, 2015 at 07:13:24PM -0400, Trond Myklebust wrote:

quoted

That makes it completely non-generic though. By putting this in the
VFS, you are giving applications a loaded gun that is pointed straight
at the application user's head.

Let me re-ask the question that I asked last week (and was apparently
ignored).  Why not trying to use the lazytime feature instead of
pointing a head straight at the application's --- and system
administrators' --- heads?

Sorry Ted, I thought I responded already.

The goal is to avoid inode writeout entirely when we can, and 
as I understand it lazytime will still force writeout before the inode 
is dropped from the cache.  In systems like Ceph in particular, the 
IOs can be spread across lots of files, so simply deferring writeout 
doesn't always help.

  Can we get some numbers on this? Before we go on and implement new mount
options, persistent inode flags, open flags, or whatever other crap
(neither of which looks particularly appealing to me) I'd like to know how
big is the performance difference between lazytime + fdatasync and not
updating mtime at all for Ceph...
								Honza
-- 
Jan Kara [off-list ref]
SUSE Labs, CR