On Thu, May 7, 2015 at 12:09 PM, Richard Weinberger <richard.weinberger@xxxxxxxxx> wrote: > On Thu, May 7, 2015 at 7:20 PM, Zach Brown <zab@xxxxxxxxxx> 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. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
