lkml.org 
[lkml]   [2015]   [Jul]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH RFC] vfs: add a O_NOMTIME flag
On Thu 2015-05-07 12:53:46, Andy Lutomirski wrote:
> On Thu, May 7, 2015 at 12:09 PM, Richard Weinberger
> <richard.weinberger@gmail.com> wrote:
> > On Thu, May 7, 2015 at 7:20 PM, Zach Brown <zab@redhat.com> wrote:
> >> On Thu, May 07, 2015 at 10:26:17AM +1000, Dave Chinner wrote:
> >>> On Wed, May 06, 2015 at 03:00:12PM -0700, Zach Brown wrote:
> >>> > Add the O_NOMTIME flag which prevents mtime from being updated which can
> >>> > greatly reduce the IO overhead of writes to allocated and initialized
> >>> > regions of files.
> >>>
> >>> Hmmm. How do backup programs now work out if the file has changed
> >>> and hence needs copying again? ie. applications using this will
> >>> break other critical infrastructure in subtle ways.
> >>
> >> By using backup infrastructure that doesn't use cmtime. Like btrfs
> >> send/recv. Or application level backups that know how to do
> >> incrementals from metadata in giant database files, say, without
> >> walking, comparing, and copying the entire thing.
> >
> > But how can Joey random user know that some of his
> > applications are using O_NOMTIME and his KISS backup
> > program does no longer function as expected?
> >
>
> Joey random user can't have a working KISS backup anyway, though,
> because we screw up mtime updates on mmap writes. I have patches
> gathering dust that fix that, though.

I'm using unison, and yes, I believe I already seen failures from
mmap(). I'd like to see that fixed, and I can test the patches.

Thanks,
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


\
 
 \ /
  Last update: 2015-07-14 14:01    [W:0.052 / U:10.400 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site