Documentation/block/writeback_cache_control.rst

2 Explicit volatile write back cache control
6 ------------
8 Many storage devices, especially in the consumer market, come with volatile
10 operating system before data actually has hit the non-volatile storage.  This
12 system needs to force data out to the non-volatile storage when it performs
21 ----------------------
24 the filesystem and will make sure the volatile cache of the storage device
26 guarantees that previously completed write requests are on non-volatile
34 ------------------
38 signaled after the data has been committed to non-volatile storage.
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51 --------------------------------------------------------------
57 drivers that do not have a volatile cache the REQ_PREFLUSH and REQ_FUA bits
58 on non-empty bios can simply be ignored, and REQ_PREFLUSH requests without
60 devices with volatile caches need to implement the support for these
65 ---------------------------------------------------------
67 For devices that do not support volatile write caches there is no driver
70 requests that have a payload.  For devices with volatile write caches the
74 	blk_queue_write_cache(sdkp->disk->queue, true, false);
82 	blk_queue_write_cache(sdkp->disk->queue, true, true);