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From:   "Finlayson, James M CIV (USA)" <james.m.finlayson4.civ@mail.mil>
To:     'Logan Gunthorpe' <logang@deltatee.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-raid@vger.kernel.org" <linux-raid@vger.kernel.org>,
        Song Liu <song@kernel.org>
CC:     Christoph Hellwig <hch@infradead.org>,
        Guoqing Jiang <guoqing.jiang@linux.dev>,
        Stephen Bates <sbates@raithlin.com>,
        "Martin Oliveira" <Martin.Oliveira@eideticom.com>,
        David Sloan <David.Sloan@eideticom.com>,
        "Finlayson, James M CIV (USA)" <james.m.finlayson4.civ@mail.mil>
Subject: RE: [Non-DoD Source] [PATCH v3 15/15] md/raid5: Increase
 restriction on max segments per request
Thread-Topic: [Non-DoD Source] [PATCH v3 15/15] md/raid5: Increase
 restriction on max segments per request
Thread-Index: AQHYgbYZzZIsZ5fz0kGRNXRewB/NQK1SjPhQ
Date:   Thu, 16 Jun 2022 21:32:21 +0000
Message-ID: <5EAED86C53DED2479E3E145969315A2389D4672D@UMECHPA68.easf.csd.disa.mil>
References: <20220616191945.23935-1-logang@deltatee.com>
 <20220616191945.23935-16-logang@deltatee.com>
In-Reply-To: <20220616191945.23935-16-logang@deltatee.com>
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Innocent question from position of ignorance....I see these last 15 check-i=
ns all as performance improvements.   I tend to push hard on mdraid perform=
ance, but have RAID6 needs....are these some optimizations available for RA=
ID6 and are they in process or did I just ask a silly question?

Regards,
Jim Finlayson
US Department of Defense

-----Original Message-----
From: Logan Gunthorpe <logang@deltatee.com>=20
Sent: Thursday, June 16, 2022 3:20 PM
To: linux-kernel@vger.kernel.org; linux-raid@vger.kernel.org; Song Liu <son=
g@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>; Guoqing Jiang <guoqing.jiang@lin=
ux.dev>; Stephen Bates <sbates@raithlin.com>; Martin Oliveira <Martin.Olive=
ira@eideticom.com>; David Sloan <David.Sloan@eideticom.com>; Logan Gunthorp=
e <logang@deltatee.com>
Subject: [Non-DoD Source] [PATCH v3 15/15] md/raid5: Increase restriction o=
n max segments per request

The block layer defaults the maximum segments to 128, which means requests =
tend to get split around the 512KB depending on how many pages can be merge=
d. There's no such restriction in the raid5 code so increase the limit to U=
SHRT_MAX so that larger requests can be sent as one.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
 drivers/md/raid5.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index e48c16bfe657..57=
23a497108a 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -8005,6 +8005,9 @@ static int raid5_run(struct mddev *mddev)
 		 */
 		blk_queue_max_hw_sectors(mddev->queue,
 			RAID5_MAX_REQ_STRIPES << RAID5_STRIPE_SHIFT(conf));
+
+		/* No restrictions on the number of segments in the request */
+		blk_queue_max_segments(mddev->queue, USHRT_MAX);
 	}
=20
 	if (log_init(conf, journal_dev, raid5_has_ppl(conf)))
--
2.30.2