On 06/19/2017 08:56 AM, Jens Axboe wrote:

On 06/19/2017 12:27 AM, Christoph Hellwig wrote:

quoted

On Sat, Jun 17, 2017 at 01:59:47PM -0600, Jens Axboe wrote:

quoted

Add four flags for the pwritev2(2) system call, allowing an application
to give the kernel a hint about what on-media life times can be
expected from a given write.

The intent is for these values to be relative to each other, no
absolute meaning should be attached to these flag names.

Set aside 3 bits in the iocb flags structure to carry this information
over from the pwritev2 RWF_WRITE_LIFE_* flags.

What is the strong use case for the per-I/O flags?  I'd much rather
stick to fcntl only for now if we can.

Fine, I guess I should just have dusted off the 2 year old patchset,
as that was _exactly_ what that did.

Actually, one good use case is O_DIRECT on a block device. Since I'm
not a huge fan of having per-call hints that is only useful for a
single case, how about we add the hints to the struct file as well?
For buffered IO, just grab it from the inode. If we have a file
available, then that overrides the per-inode setting.


-- 
Jens Axboe