linux-kernel - Re: [dm-devel] [PATCH v2 1/1] block: fix blk_queue

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Date:	Tue, 12 Jul 2016 12:55:10 +1000
From:	NeilBrown <neilb@...e.com>
To:	Lars Ellenberg <lars.ellenberg@...bit.com>,
	Jens Axboe <axboe@...nel.dk>
Cc:	linux-block@...r.kernel.org,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Mike Snitzer <snitzer@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Ming Lei <ming.lei@...onical.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
	Takashi Iwai <tiwai@...e.de>, linux-bcache@...r.kernel.org,
	Zheng Liu <gnehzuil.liu@...il.com>,
	Kent Overstreet <kent.overstreet@...il.com>,
	Keith Busch <keith.busch@...el.com>, dm-devel@...hat.com,
	Shaohua Li <shli@...nel.org>, Ingo Molnar <mingo@...hat.com>,
	Alasdair Kergon <agk@...hat.com>,
	Roland Kammerer <roland.kammerer@...bit.com>
Subject: Re: [dm-devel] [PATCH v2 1/1] block: fix blk_queue_split() resource	exhaustion

On Tue, Jul 12 2016, Lars Ellenberg wrote:
....
>
> Instead, I suggest to distinguish between recursive calls to
> generic_make_request(), and pushing back the remainder part in
> blk_queue_split(), by pointing current->bio_lists to a
> 	struct recursion_to_iteration_bio_lists {
> 		struct bio_list recursion;
> 		struct bio_list queue;
> 	}
>
> By providing each q->make_request_fn() with an empty "recursion"
> bio_list, then merging any recursively submitted bios to the
> head of the "queue" list, we can make the recursion-to-iteration
> logic in generic_make_request() process deepest level bios first,
> and "sibling" bios of the same level in "natural" order.
>
> Signed-off-by: Lars Ellenberg <lars.ellenberg@...bit.com>
> Signed-off-by: Roland Kammerer <roland.kammerer@...bit.com>

Reviewed-by: NeilBrown <neilb@...e.com>

Thanks again for doing this - I think this is a very significant
improvement and could allow other simplifications.

NeilBrown

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