lkml.org 
[lkml]   [2014]   [Oct]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC PATCH 0/5] Enable use of Solid State Hybrid Drives
On Wed, Oct 29, 2014 at 11:23:38AM -0700, Jason B. Akers wrote:
> The following series enables the use of Solid State hybrid drives
> ATA standard 3.2 defines the hybrid information feature, which provides a means for the host driver to provide hints to the SSHDs to guide what to place on the SSD/NAND portion and what to place on the magnetic media.
>
> This implementation allows user space applications to provide the cache hints to the kernel using the existing ionice syscall.
>
> An application can pass a priority number coding up bits 11, 12, and 15 of the ionice command to form a 3 bit field that encodes the following priorities:
> OPRIO_ADV_NONE,
> IOPRIO_ADV_EVICT, /* actively discard cached data */
> IOPRIO_ADV_DONTNEED, /* caching this data has little value */
> IOPRIO_ADV_NORMAL, /* best-effort cache priority (default) */
> IOPRIO_ADV_RESERVED1, /* reserved for future use */
> IOPRIO_ADV_RESERVED2,
> IOPRIO_ADV_RESERVED3,
> IOPRIO_ADV_WILLNEED, /* high temporal locality */
>
> For example the following commands from the user space will make dd IOs to be generated with a hint of IOPRIO_ADV_DONTNEED assuming the SSHD is /dev/sdc.
>
> ionice -c2 -n4096 dd if=/dev/zero of=/dev/sdc bs=1M count=1024
> ionice -c2 -n4096 dd if=/dev/sdc of=/dev/null bs=1M count=1024

This looks to be the wrong way to implement per-IO priority
information.

How does a filesystem make use of this to make sure it's
metadata ends up with IOPRIO_ADV_WILLNEED to store frequently
accessed metadata in flash. Conversely, journal writes need to
be issued with IOPRIO_ADV_DONTNEED so they don't unneceessarily
consume flash space as they are never-read IOs...

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com


\
 
 \ /
  Last update: 2014-10-29 21:21    [W:0.172 / U:0.040 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site