From: Steffen Maier <maier@linux.ibm.com> To: Ming Lei <ming.lei@redhat.com> Cc: linux-scsi@vger.kernel.org, "Martin K . Petersen" <martin.petersen@oracle.com>, James Bottomley <James.Bottomley@hansenpartnership.com>, Bart Van Assche <bvanassche@acm.org>, Hannes Reinecke <hare@suse.com>, Christoph Hellwig <hch@lst.de>, Jim Gill <jgill@vmware.com>, Cathy Avery <cavery@redhat.com>, "Ewan D . Milne" <emilne@redhat.com>, Brian King <brking@us.ibm.com>, James Smart <james.smart@broadcom.com>, "Juergen E . Fischer" <fischer@norbit.de>, Michael Schmitz <schmitzmic@gmail.com>, Finn Thain <fthain@telegraphics.com.au>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, devel@driverdev.osuosl.org, linux-usb@vger.kernel.org, Dan Carpenter <dan.carpenter@oracle.com>, Benjamin Block <bblock@linux.ibm.com>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Heiko Carstens <heiko.carstens@de.ibm.com>, linux-s390@vger.kernel.org Subject: Re: [PATCH V5 10/16] s390: zfcp_fc: use sg helper to operate scatterlist Date: Wed, 26 Jun 2019 10:17:33 +0200 Message-ID: <1353d755-de62-d575-4c7b-d20d59d07f23@linux.ibm.com> (raw) In-Reply-To: <20190626030751.GA26340@ming.t460p> Hi Ming, On 6/26/19 5:07 AM, Ming Lei wrote: > On Tue, Jun 25, 2019 at 12:51:04PM +0200, Steffen Maier wrote: >> I don't mind doing this change for zfcp. However, I'm having doubts >> regarding the rationale in the commit description. > However, I still suggest to do it because it will make us to audit SCSI chained > sg uses much easier. And the change shouldn't have performance effect. >> If I was not mistaken above, the following could be more descriptive parts >> of a patch/commit description, with hopefully less confusion for anyone >> having to look at zfcp git history a few weeks/months/years from now: >> >> "While not required for this SCSI MQ change regarding scatterlist >> allocation, change all other scatterlist iterators in zfcp to the safe >> sg_next() even if not necessary as these changed zfcp-internal scatterlists >> are linear and unchained. This may avoid confusion about a potential need >> for conversions in the future." Sure, let's change the code, but could you please update the description of your below new patch to something like I drafted above regarding rationale? If you would like to send a V2, I'll be happy to give a Reviewed-by. >>> From c9c368308fefbf034d670984fe9746a4181fe514 Mon Sep 17 00:00:00 2001 >>> From: Ming Lei <ming.lei@redhat.com> >>> Date: Tue, 25 Jun 2019 09:15:34 +0800 >>> Subject: [PATCH] s390: scsi: use sg helper to iterate over scatterlist >>> Unlike the legacy I/O path, scsi-mq preallocates a large array to hold >>> the scatterlist for each request. This static allocation can consume >>> substantial amounts of memory on modern controllers which support a >>> large number of concurrently outstanding requests. >>> To facilitate a switch to a smaller static allocation combined with a >>> dynamic allocation for requests that need it, we need to make sure all >>> SCSI drivers handle chained scatterlists correctly. >>> Convert remaining drivers that directly dereference the scatterlist >>> array to using the iterator functions. > OK, I still suggest to apply the patch for the mentioned reason if you > are fine. -- Mit freundlichen Gruessen / Kind regards Steffen Maier Linux on IBM Z Development https://www.ibm.com/privacy/us/en/ IBM Deutschland Research & Development GmbH Vorsitzender des Aufsichtsrats: Matthias Hartmann Geschaeftsfuehrung: Dirk Wittkopp Sitz der Gesellschaft: Boeblingen Registergericht: Amtsgericht Stuttgart, HRB 243294
next prev parent reply index Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-06-18 1:37 [PATCH V5 00/16] " Ming Lei 2019-06-18 1:37 ` [PATCH V5 01/16] scsi: vmw_pscsi: " Ming Lei 2019-06-18 1:37 ` [PATCH V5 02/16] scsi: advansys: " Ming Lei 2019-06-18 1:37 ` [PATCH V5 03/16] scsi: lpfc: " Ming Lei 2019-06-18 1:37 ` [PATCH V5 04/16] scsi: mvumi: " Ming Lei 2019-06-18 1:37 ` [PATCH V5 05/16] scsi: ipr: " Ming Lei 2019-06-18 1:37 ` [PATCH V5 06/16] scsi: pmcraid: " Ming Lei 2019-06-18 1:37 ` [PATCH V5 07/16] usb: image: microtek: " Ming Lei 2019-06-18 1:37 ` [PATCH V5 08/16] staging: unisys: visorhba: " Ming Lei 2019-06-18 1:37 ` [PATCH V5 09/16] staging: rtsx: " Ming Lei 2019-06-18 1:37 ` [PATCH V5 10/16] s390: zfcp_fc: " Ming Lei 2019-06-24 15:13 ` Steffen Maier 2019-06-25 1:19 ` Ming Lei 2019-06-25 2:01 ` Finn Thain 2019-06-25 2:30 ` Ming Lei 2019-06-25 3:42 ` Finn Thain 2019-06-25 10:51 ` Steffen Maier 2019-06-26 3:07 ` Ming Lei 2019-06-26 8:17 ` Steffen Maier [this message] 2019-06-18 1:37 ` [PATCH V5 11/16] scsi: aha152x: " Ming Lei 2019-06-18 3:54 ` Finn Thain 2019-06-18 1:37 ` [PATCH V5 12/16] scsi: imm: " Ming Lei 2019-06-18 1:37 ` [PATCH V5 13/16] scsi: pcmcia: nsp_cs: " Ming Lei 2019-06-18 1:37 ` [PATCH V5 14/16] scsi: ppa: " Ming Lei 2019-06-18 1:37 ` [PATCH V5 15/16] scsi: wd33c93: " Ming Lei 2019-06-18 1:37 ` [PATCH V5 16/16] NCR5380: Support chained sg lists Ming Lei 2019-06-19 0:29 ` [PATCH V5 00/16] use sg helper to operate scatterlist Martin K. Petersen 2019-06-19 19:43 ` Bart Van Assche 2019-06-19 19:55 ` Martin K. Petersen 2019-06-24 12:40 ` Ming Lei 2019-06-24 12:54 ` Martin K. Petersen
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