[lkml]   [2010]   [Aug]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCHSET block#for-2.6.36-post] block: replace barrier with sequenced flush

On 08/20/2010 03:22 PM, Christoph Hellwig wrote:
> Many storage devices, especially in the consumer market, come with volatile
> write back caches. That means the devices signal I/O completion to the
> operating system before data actually has hit the physical medium.

A bit nit picky but flash devices can also have writeback caches and
the term physical medium sounds a bit off for those cases. Maybe just
saying "non-volatile media" is better?

> Implementation details for filesystems
> --------------------------------------
> Filesystem can simply set the REQ_FLUSH and REQ_FUA bits and do not have to
> worry if the underlying devices need any explicit cache flushing and how
> the Forced Unit Access is implemented. The REQ_FLUSH and REQ_FUA flags
> may both be set on a single bio.

It may be worthwhile to explain the sequence of operations when
REQ_FLUSH + data + REQ_FUA is executed. It can be extrapolated from
the previous two descriptions but I think giving examples of different
sequences depending on FLUSH/FUA configuration would be helpful to
help understanding the overall picture of things.

Other than those, looks good to me.



 \ /
  Last update: 2010-08-23 14:45    [W:0.308 / U:1.288 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site