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Date: Tue, 25 Jan 2011 15:46:06 -0500 From: Vivek Goyal <vgoyal@...hat.com> To: Tejun Heo <tj@...nel.org> Cc: Mike Snitzer <snitzer@...hat.com>, axboe@...nel.dk, tytso@....edu, djwong@...ibm.com, shli@...nel.org, neilb@...e.de, adilger.kernel@...ger.ca, jack@...e.cz, linux-kernel@...r.kernel.org, kmannth@...ibm.com, cmm@...ibm.com, linux-ext4@...r.kernel.org, rwheeler@...hat.com, hch@....de, josef@...hat.com Subject: Re: [PATCH 3/3] block: reimplement FLUSH/FUA to support merge 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 -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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