lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAHQdGtS0=Gjyq2E2QO+zu_HAzdrHJwxtfZ8MB5q0DjWHMEc7hw@mail.gmail.com>
Date:	Wed, 6 May 2015 18:14:34 -0400
From:	Trond Myklebust <trond.myklebust@...marydata.com>
To:	Zach Brown <zab@...hat.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Sage Weil <sweil@...hat.com>,
	Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux API Mailing List <linux-api@...r.kernel.org>
Subject: Re: [PATCH RFC] vfs: add a O_NOMTIME flag

Hi Zach,

On Wed, May 6, 2015 at 6:00 PM, Zach Brown <zab@...hat.com> 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.
>
> ceph servers can have loads where they perform O_DIRECT overwrites of
> allocated file data and then sync to make sure that the O_DIRECT writes
> are flushed from write caches.  If the writes dirty the inode with mtime
> updates then the syncs also write out the metadata needed to track the
> inodes which can add significant iop and latency overhead.
>
> The ceph servers don't use mtime at all.  They're using the local file
> system as a backing store and any backups would be driven by their upper
> level ceph metadata.  For ceph, slow IO from mtime updates in the file
> system is as daft as if we had block devices slowing down IO for
> per-block write timestamps that file systems never use.
>
> In simple tests a O_DIRECT|O_NOMTIME overwriting write followed by a
> sync went from 2 serial write round trips to 1 in XFS and from 4 serial
> IO round trips to 1 in ext4.
>
> file_update_time() checks for O_NOMTIME and aborts the update if it's
> set, just like the current check for the in-kernel inode flag
> S_NOCMTIME.  I didn't update any other mtime update sites. They could be
> added as we decide that it's appropriate to do so.
>
> I opted not to name the flag O_NOCMTIME because I didn't want the name
> to imply that ctime updates would be prevented for other inode changes
> like updating i_size in truncate.  Not updating ctime is a side-effect
> of removing mtime updates when it's the only thing changing in the
> inode.
>
> The criteria for using O_NOMTIME is the same as for using O_NOATIME:
> owning the file or having the CAP_FOWNER capability.  If we're not
> comfortable allowing owners to prevent mtime/ctime updates then we
> should add a tunable to allow O_NOMTIME.  Maybe a mount option?
>

Just out of curiosity, if you need to modify the application anyway,
why wouldn't use of fdatasync() when flushing be able to offer a
similar performance boost?

Cheers
  Trond
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ