From: Ming Lei <ming.lei@redhat.com>
To: Guenter Roeck <linux@roeck-us.net>
Cc: James Bottomley <James.Bottomley@hansenpartnership.com>,
linux-scsi@vger.kernel.org,
"Martin K . Petersen" <martin.petersen@oracle.com>,
linux-block@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
Bart Van Assche <bvanassche@acm.org>,
"Ewan D . Milne" <emilne@redhat.com>,
Hannes Reinecke <hare@suse.com>
Subject: Re: [PATCH V4 3/3] scsi: core: avoid to pre-allocate big chunk for sg list
Date: Tue, 4 Jun 2019 09:00:03 +0800 [thread overview]
Message-ID: <20190604010002.GA24432@ming.t460p> (raw)
In-Reply-To: <20190603204422.GA7240@roeck-us.net>
On Mon, Jun 03, 2019 at 01:44:22PM -0700, Guenter Roeck wrote:
> On Sun, Apr 28, 2019 at 03:39:32PM +0800, Ming Lei wrote:
> > Now scsi_mq_setup_tags() pre-allocates a big buffer for IO sg list,
> > and the buffer size is scsi_mq_sgl_size() which depends on smaller
> > value between shost->sg_tablesize and SG_CHUNK_SIZE.
> >
> > Modern HBA's DMA is often capable of deadling with very big segment
> > number, so scsi_mq_sgl_size() is often big. Suppose the max sg number
> > of SG_CHUNK_SIZE is taken, scsi_mq_sgl_size() will be 4KB.
> >
> > Then if one HBA has lots of queues, and each hw queue's depth is
> > high, pre-allocation for sg list can consume huge memory.
> > For example of lpfc, nr_hw_queues can be 70, each queue's depth
> > can be 3781, so the pre-allocation for data sg list is 70*3781*2k
> > =517MB for single HBA.
> >
> > There is Red Hat internal report that scsi_debug based tests can't
> > be run any more since legacy io path is killed because too big
> > pre-allocation.
> >
> > So switch to runtime allocation for sg list, meantime pre-allocate 2
> > inline sg entries. This way has been applied to NVMe PCI for a while,
> > so it should be fine for SCSI too. Also runtime sg entries allocation
> > has verified and run always in the original legacy io path.
> >
> > Not see performance effect in my big BS test on scsi_debug.
> >
>
> This patch causes a variety of boot failures in -next. Typical failure
> pattern is scsi hangs or failure to find a root file system. For example,
> on alpha, trying to boot from usb:
I guess it is because alpha doesn't support sg chaining, and
CONFIG_ARCH_NO_SG_CHAIN is enabled. ARCHs not supporting sg chaining
can only be arm, alpha and parisc.
Please test the following patch and see if it makes a difference:
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 6e81258471fa..9ef632963740 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -44,9 +44,13 @@
* Size of integrity metadata is usually small, 1 inline sg should
* cover normal cases.
*/
+#ifndef CONFIG_ARCH_NO_SG_CHAIN
#define SCSI_INLINE_PROT_SG_CNT 1
-
#define SCSI_INLINE_SG_CNT 2
+#else
+#define SCSI_INLINE_PROT_SG_CNT 0
+#define SCSI_INLINE_SG_CNT 0
+#endif
static struct kmem_cache *scsi_sdb_cache;
static struct kmem_cache *scsi_sense_cache;
Thanks,
Ming
next prev parent reply other threads:[~2019-06-04 1:00 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-28 7:39 [PATCH V4 0/3] scsi: core: avoid big pre-allocation for sg list Ming Lei
2019-04-28 7:39 ` [PATCH V4 1/3] lib/sg_pool.c: improve APIs for allocating sg pool Ming Lei
2019-04-28 12:04 ` Christoph Hellwig
2019-04-28 7:39 ` [PATCH V4 2/3] scsi: core: avoid to pre-allocate big chunk for protection meta data Ming Lei
2019-04-29 18:15 ` Bart Van Assche
2019-04-28 7:39 ` [PATCH V4 3/3] scsi: core: avoid to pre-allocate big chunk for sg list Ming Lei
2019-04-29 18:16 ` Bart Van Assche
2019-06-03 20:44 ` Guenter Roeck
2019-06-04 1:00 ` Ming Lei [this message]
2019-06-04 3:49 ` Guenter Roeck
2019-06-04 4:10 ` Ming Lei
2019-06-04 14:51 ` Guenter Roeck
2019-06-04 6:55 ` Ming Lei
2019-05-05 1:10 ` [PATCH V4 0/3] scsi: core: avoid big pre-allocation " Ming Lei
2019-05-14 2:06 ` Martin K. Petersen
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