linux-kernel - Re: [PATCHSET block#for-2.6.36-post] block: replace barrier with sequenced flush

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Message-ID: <20100819102023.GA6736@lst.de>
Date:	Thu, 19 Aug 2010 12:20:23 +0200
From:	Christoph Hellwig <hch@....de>
To:	Tejun Heo <tj@...nel.org>
Cc:	Christoph Hellwig <hch@....de>, jaxboe@...ionio.com,
	linux-fsdevel@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-raid@...r.kernel.org, James.Bottomley@...e.de, tytso@....edu,
	chris.mason@...cle.com, swhiteho@...hat.com,
	konishi.ryusuke@....ntt.co.jp, dm-devel@...hat.com, vst@...b.net,
	jack@...e.cz, rwheeler@...hat.com, hare@...e.de
Subject: Re: [PATCHSET block#for-2.6.36-post] block: replace barrier with sequenced flush

On Thu, Aug 19, 2010 at 11:57:53AM +0200, Tejun Heo wrote:
> On 08/18/2010 11:46 AM, Christoph Hellwig wrote:
> > FYI: One issue with this series is that make_request based drivers
> > not have to access all REQ_FLUSH and REQ_FUA requests.  We'll either
> > need to add handling to empty REQ_FLUSH requests to all of them or
> > figure out a way to prevent them getting sent.  That is assuming they'll
> > simply ignore REQ_FLUSH/REQ_FUA on normal writes.
> 
> Can you be a bit more specific?  In most cases, request based drivers
> should be fine.  They sit behind the front most request_queue which
> would discompose REQ_FLUSH/FUAs into appropriate command sequence.

I said make_request based drivers, that is drivers taking bios.   These
get bios directly from __generic_make_request and need to deal with
REQ_FLUSH/FUA themselves.  We have quite a few more than just dm/md of
this kind:

arch/powerpc/sysdev/axonram.c:	blk_queue_make_request(bank->disk->queue, axon_ram_make_request);
drivers/block/aoe/aoeblk.c:     blk_queue_make_request(d->blkq, aoeblk_make_request);
drivers/block/brd.c:		blk_queue_make_request(brd->brd_queue, brd_make_request);
drivers/block/drbd/drbd_main.c: blk_queue_make_request(q, drbd_make_request_26);
drivers/block/loop.c:		blk_queue_make_request(lo->lo_queue, loop_make_request);
drivers/block/pktcdvd.c:        blk_queue_make_request(q, pkt_make_request);
drivers/block/ps3vram.c:        blk_queue_make_request(queue, ps3vram_make_request);
drivers/block/umem.c:		blk_queue_make_request(card->queue, mm_make_request);
drivers/s390/block/dcssblk.c:	blk_queue_make_request(dev_info->dcssblk_queue, dcssblk_make_request);
drivers/s390/block/xpram.c:	blk_queue_make_request(xpram_queues[i], xpram_make_request);
drivers/staging/zram/zram_drv.c:blk_queue_make_request(zram->queue, zram_make_request);


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