Re: [dm-devel] [PATCH v2 1/1] block: fix blk_queue_split() resource exhaustion

From: NeilBrown <neilb@suse.com>
To: Lars Ellenberg <lars.ellenberg@linbit.com>, Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Mike Snitzer <snitzer@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Jiri Kosina <jkosina@suse.cz>, Ming Lei <ming.lei@canonical.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org,
	Takashi Iwai <tiwai@suse.de>,
	linux-bcache@vger.kernel.org, Zheng Liu <gnehzuil.liu@gmail.com>,
	Kent Overstreet <kent.overstreet@gmail.com>,
	Keith Busch <keith.busch@intel.com>,
	dm-devel@redhat.com, Shaohua Li <shli@kernel.org>,
	Ingo Molnar <mingo@redhat.com>, Alasdair Kergon <agk@redhat.com>,
	Roland Kammerer <roland.kammerer@linbit.com>
Subject: Re: [dm-devel] [PATCH v2 1/1] block: fix blk_queue_split() resource	exhaustion
Date: Tue, 12 Jul 2016 12:55:10 +1000	[thread overview]
Message-ID: <87lh17efap.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <20160711141042.GY13335@soda.linbit>

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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@linbit.com>
> Signed-off-by: Roland Kammerer <roland.kammerer@linbit.com>

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

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

NeilBrown

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