On Wed, Aug 13, 2014 at 8:55 PM, Emmanuel Dreyfus <manu@xxxxxxxxxx> wrote:
Anand Avati <avati@xxxxxxxxxxx> wrote:I am not sure what could make a FS decide that for the same file, one
> That may / may not work well in practice depending on the number of
> concurrent apps working on a file.
file descriptor should use direct I/O and another should not.
Keeping the flag at file descriptor level would require VFS modification
in the kernel: the filesystem knows nothing about file descriptors, it
just know vnodes. It could be done, but I expect to meet resistance :-)
For e.g, glusterfs used to enable directio mode for non-read-only FDs (to cut overheads) but disable directio for read-only (to leverage readahead). After big_writes was introduced in Linux FUSE this has changed.
But we should be OK having vnode level switch for now, I think.
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