On Tue, Sep 03, 2024 at 07:58:46PM GMT, Kanchan Joshi wrote:

Hi Amir,


On 8/26/2024 10:36 PM, Kanchan Joshi wrote:

quoted

Current write-hint infrastructure supports 6 temperature-based data life
hints.
The series extends the infrastructure with a new temperature-agnostic
placement-type hint. New fcntl codes F_{SET/GET}_RW_HINT_EX allow to
send the hint type/value on file. See patch #3 commit description for
the details.

Overall this creates 128 placement hint values [*] that users can pass.
Patch #5 adds the ability to map these new hint values to nvme-specific
placement-identifiers.
Patch #4 restricts SCSI to use only life hint values.
Patch #1 and #2 are simple prep patches.

[*] While the user-interface can support more, this limit is due to the
in-kernel plumbing consideration of the inode size. Pahole showed 32-bit
hole in the inode, but the code had this comment too:

/* 32-bit hole reserved for expanding i_fsnotify_mask */

Not must, but it will be good to know if a byte (or two) can be used
here.

Since having one extra byte will simplify things, I can't help but ask - 
do you still have the plans to use this space (in entirety) within inode?

I just freed up 8 bytes in struct inode with what's currently in -next.
There will be no using up those 8 bytes unless it's for a good reason 
and something that is very widely useful.