Hello, 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. Thanks. -- tejun -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
