Messages in this thread | | | Date | Tue, 25 Jan 2011 15:46:06 -0500 | From | Vivek Goyal <> | Subject | Re: [PATCH 3/3] block: reimplement FLUSH/FUA to support merge |
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On Sun, Jan 23, 2011 at 11:31:33AM +0100, Tejun Heo wrote: > On Fri, Jan 21, 2011 at 07:49:55PM -0500, Mike Snitzer wrote: > > > + * If the device doesn't have writeback cache, FLUSH and FUA don't make any > > > + * difference. The requests are either completed immediately if there's no > > > + * data or executed as normal requests otherwise. > > > > For devices without a writeback cache, I'm not seeing where pure flushes > > are completed immediately. But I do see where data is processed > > directly in blk_insert_flush(). > > Yeah, it does. Pure flushes on a device w/o writeback cache, @policy > is zero and blk_flush_complete_seq() will directly proceed to > REQ_FSEQ_DONE.
I see following code in __generic_make_request(). I am wondering if empty flushes will be completed here itself if device does not have writeback cache.
/* * Filter flush bio's early so that make_request based * drivers without flush support don't have to worry * about them. */ if ((bio->bi_rw & (REQ_FLUSH | REQ_FUA)) && !q->flush_flags) { bio->bi_rw &= ~(REQ_FLUSH | REQ_FUA); if (!nr_sectors) { err = 0; goto end_io; } }
Thanks Vivek
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