On 10/03/2012 08:50 AM, Paolo Bonzini wrote:
Il 24/09/2012 11:13, Bharata B Rao ha scritto:+ + if ((bdrv_flags& BDRV_O_NOCACHE)) { + open_flags |= O_DIRECT; + } +If I understand correctly what I was told, this prevents the brick server from using its own buffer cache. This is quite different from what we do for example over NFS (where the host does no caching, but nothing prevents it on the remote server). I think these 3 lines should be removed. We're bypassing the host buffer cache just by virtue of using a userspace driver, and that's what cache=none cares about. Paolo
O_DIRECT also has an effect on the behavior of the "client side" (the part within the qemu) of Gluster stack as well. I presume the intention of O_DIRECT is to minimize use of memory (whether as host' page cache or buffered data in user space). To that end it is a good idea to leave O_DIRECT flag set.
The behavior of whether gluster bricks need to get the O_DIRECT propagated or not is a different issue. We are exploring the possibility of not sending O_DIRECT flag over the wire to mimic NFS behavior. That would be independent of the qemu block driver setting the open flag.
Avati
