On Wed 23-01-19 19:27:12, Javier González wrote:

quoted

On 9 Jan 2019, at 16.30, Kanchan Joshi [off-list ref] wrote:

Exiting write-hints are exposed to user-mode. There is a possiblity
of conflict if kernel happens to use those. This patch introduces four
write-hints for exclusive kernel-mode use.

Signed-off-by: Kanchan Joshi <redacted>
---
include/linux/fs.h | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 811c777..e8548eb 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h

@@ -291,6 +291,11 @@ enum rw_hint {

	WRITE_LIFE_MEDIUM	= RWH_WRITE_LIFE_MEDIUM,
	WRITE_LIFE_LONG		= RWH_WRITE_LIFE_LONG,
	WRITE_LIFE_EXTREME	= RWH_WRITE_LIFE_EXTREME,
+/* below ones are meant for in-kernel use */
+	KERN_WRITE_LIFE_SHORT,
+	KERN_WRITE_LIFE_MEDIUM,
+	KERN_WRITE_LIFE_LONG,
+	KERN_WRITE_LIFE_EXTREME
};

I think Jens and Dave meant kernel hints to go top down. This would also
give space for supporting more hints / streams from both ends for user
and kernel.

Yes, that was the idea however if I understand it right, the write hints do
not really have to be consistent boot-to-boot since they aren't stored
persistently by the disk, are they? If that's the case, it doesn't really
matter which numbers we pick.

One thing I don't quite like is the naming of KERN_WRITE_LIFE_SHORT etc.. It
is upto filesystem to assign meanings to the write hints. So I think it is
enough to provide something like KERN_WRITE_HINT_MIN which is the first
hint available to the kernel and then the number of hints available to the
kernel.

								Honza

-- 
Jan Kara [off-list ref]
SUSE Labs, CR