On Wed, 01 Apr 2015 12:24:38 -0600 Eric Mei <meijia@xxxxxxxxx> wrote: > I can see how FUA is handled, but REQ_FLUSH seems problematic. My > understanding of REQ_FLUSH semantics: all requests before the flush > request must *complete* before the flush request complete. For IO remap > layer like MD, we need to guarantee all previous requests are > *submitted* to component devices before submitting the flush request. Is > that correct? No. See Documentation/block/writeback_cache_control.txt Only "previously completed" requests are affect by REQ_FLUSH. So any code using REQ_FLUSH must first wait for previous requests to complete, and then submit REQ_FLUSH. The REQ_FLUSH will not return until the data written by those requests is actually in stable storage, rather than write-behind cache. NeilBrown > > If so why I don't see the code which make sure the pending write > requests in stripe cache are processed & submitted before > submit_flushes() get called? Thanks > > Eric > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html
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