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From: Christoph Hellwig <hch@lst.de>
To: Benjamin Block <bblock@linux.ibm.com>
Cc: Christoph Hellwig <hch@lst.de>,
	Matthew Wilcox <willy@infradead.org>,
	Jens Axboe <axboe@kernel.dk>, Khalid Aziz <khalid@gonehiking.org>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Hannes Reinecke <hare@suse.com>,
	Ondrej Zary <linux@rainbow-software.org>,
	linux-block@vger.kernel.org, linux-scsi@vger.kernel.org
Subject: Re: [PATCH 7/8] block: refactor the bounce buffering code
Date: Wed, 24 Mar 2021 18:44:58 +0100	[thread overview]
Message-ID: <20210324174458.GA13589@lst.de> (raw)
In-Reply-To: <YFt5kPs30x4kPu77@t480-pf1aa2c2.linux.ibm.com>

On Wed, Mar 24, 2021 at 06:40:32PM +0100, Benjamin Block wrote:
> Is blk_queue_bounce() called again when mpath submits the request to the
> lower device? I thought when I looked at this code some time ago
> bouncing would only be checked the first time a request is created
> (dm-mpath), and then not again, so when we don't check for whether
> bouncing is necessary in mpath, we still might screw the LLD - hence why
> we might inherit this via the limits.

Every call to blk_mq_submit_bio also calls blk_queue_bounce, and
blk_queue_bounce then checks if it needs to do anything based on the
bounce limit and max_pfn, and if needed proceeds to check every bvec.

So for extremely unlikely case thay someone is running multipath over one
of the few remaining drivers that need block layering bounce buffering
this inheritance just leads to (harmless) extra work.

  reply	other threads:[~2021-03-24 17:45 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-18  6:39 start removing block bounce buffering support Christoph Hellwig
2021-03-18  6:39 ` [PATCH 1/8] aha1542: use a local bounce buffer Christoph Hellwig
2021-03-18  6:39 ` [PATCH 2/8] Buslogic: remove ISA support Christoph Hellwig
2021-03-18  6:39 ` [PATCH 3/8] BusLogic: reject broken old firmware that requires ISA-style bounce buffering Christoph Hellwig
2021-03-18  6:39 ` [PATCH 4/8] advansys: remove ISA support Christoph Hellwig
2021-03-18 11:20   ` Matthew Wilcox
2021-03-18 12:54     ` Christoph Hellwig
2021-03-18 14:34       ` Matthew Wilcox
2021-03-18  6:39 ` [PATCH 5/8] scsi: remove the unchecked_isa_dma flag Christoph Hellwig
2021-03-18  6:39 ` [PATCH 6/8] block: remove BLK_BOUNCE_ISA support Christoph Hellwig
2021-03-18  6:39 ` [PATCH 7/8] block: refactor the bounce buffering code Christoph Hellwig
2021-03-18 11:29   ` Matthew Wilcox
2021-03-18 12:53     ` Christoph Hellwig
2021-03-24 17:40       ` Benjamin Block
2021-03-24 17:44         ` Christoph Hellwig [this message]
2021-03-24 18:07           ` Benjamin Block
2021-03-24 18:13             ` Christoph Hellwig
2021-03-18  6:39 ` [PATCH 8/8] block: stop calling blk_queue_bounce for passthrough requests Christoph Hellwig
2021-03-26  5:58 start removing block bounce buffering support v2 Christoph Hellwig
2021-03-26  5:58 ` [PATCH 7/8] block: refactor the bounce buffering code Christoph Hellwig
2021-03-29  6:34   ` Hannes Reinecke
2021-03-31  7:29 start removing block bounce buffering support v3 Christoph Hellwig
2021-03-31  7:30 ` [PATCH 7/8] block: refactor the bounce buffering code Christoph Hellwig

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