linux-kernel - [PATCH] scsi: sd: Add a comment about limiting max

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Date:   Tue, 19 Jul 2022 17:51:04 +0800
From:   John Garry <john.garry@...wei.com>
To:     <jejb@...ux.ibm.com>, <martin.petersen@...cle.com>, <hch@....de>,
        <damien.lemoal@...nsource.wdc.com>
CC:     <linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <iommu@...ts.linux.dev>, John Garry <john.garry@...wei.com>
Subject: [PATCH] scsi: sd: Add a comment about limiting max_sectors to shost optimal limit

Add a comment about limiting the default the SCSI disk request_queue
max_sectors initial value to that of the SCSI host optimal sectors limit.

Suggested-by: Damien Le Moal <damien.lemoal@...nsource.wdc.com>
Signed-off-by: John Garry <john.garry@...wei.com>

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 3eaee1f7aaca..ed9f43f9512e 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -3296,6 +3296,11 @@ static int sd_revalidate_disk(struct gendisk *disk)
 				      (sector_t)BLK_DEF_MAX_SECTORS);
 	}
 
+	/*
+	 * Limit default to SCSI host optimal sector limit if set. There may be
+	 * an impact on performance for when the size of a request exceeds this
+	 * host limit.
+	 */
 	rw_max = min_not_zero(rw_max, sdp->host->opt_sectors);
 
 	/* Do not exceed controller limit */
-- 
2.35.3