linux-kernel - Re: [PATCH v2] block: make sure big bio is splitted into at most 256 bvecs

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Date:	Mon, 13 Jun 2016 08:46:14 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Hannes Reinecke <hare@...e.de>
Cc:	Ming Lei <ming.lei@...onical.com>, Jens Axboe <axboe@...com>,
	linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Kent Overstreet <kent.overstreet@...il.com>,
	"4.3+" <stable@...r.kernel.org>, Shaohua Li <shli@...com>,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v2] block: make sure big bio is splitted into at most 256
 bvecs

On Fri, Jun 10, 2016 at 01:37:17PM +0200, Hannes Reinecke wrote:
> Hmm. So everybody is suffering because someone _might_ be using bio_clone?
> Why can't we fixup bio_clone() (or the callers of which) to correctly
> set the queue limits?

The only one suffering is bcache.  Everyone else uses bios below the
block layer arbitrary max size.  The fixup to allow bio_clone support
a larger size is the same one as to allow everyone else submitting
larger bios:  increase BIO_MAX_PAGES and create the required mempools
to back that new larger size.  Or just go for multipage biovecs..