[sheepdog] [PATCH] disk cache: drop O_DSYNC only when O_DIRECT is set
morita.kazutaka at lab.ntt.co.jp
Tue Oct 30 12:16:46 CET 2012
At Tue, 30 Oct 2012 18:30:37 +0800,
Liu Yuan wrote:
> On 10/30/2012 08:49 AM, MORITA Kazutaka wrote:
> > At Thu, 25 Oct 2012 13:52:01 +0900,
> > MORITA Kazutaka wrote:
> >> To make sure that data is not cached by the host os, we cannot drop
> >> O_DSYNC when O_DIRECT is not set.
> Why data are cached in page cache a problem? We do sync(2) it afterwards.
For users who run VMs on storage nodes, more memory should be used for
guest OSes. It's inefficient to cache data in both host and guest
> We don't set O_DIRECT for inode object, so sync(2) won't flush it to
> disk safely?
O_DIRECT imposes alignment restrictions on both the file offset and
the buffer length, so we cannot use it for any files other than data
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