Re: [PATCH v5 2/2] Add support for SCT Write Same

From	"Martin K. Petersen" <martin.petersen@oracle.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v5 2/2] Add support for SCT Write Same
Date	2016-08-11 03:50 +0200
Message-ID	<s4Ni9-4Db-1@gated-at.bofh.it> (permalink)
References	(1 earlier) <s4qbT-6NI-3@gated-at.bofh.it> <s4Gqo-b4-133@gated-at.bofh.it> <s4Gqo-b4-135@gated-at.bofh.it> <s4Gqo-b4-137@gated-at.bofh.it> <s4Gqo-b4-139@gated-at.bofh.it>
Organization	Oracle Corporation

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>>>>> "Tom" == Tom Yan <tom.ty89@gmail.com> writes:

Tom> Well that is actually the minimum. Modern SSDs often support more
Tom> than one-block payload (e.g. 8, 16...).  It's just our SCSI disk
Tom> driver statically limit it to the minimum. Though it allows only
Tom> 0xffffffff / 512 = 8388607 (SD_MAX_WS16_BLOCKS) blocks per WRITE
Tom> SAME (16) command anyway,

Yes, because that's the biggest command we can express in the block
layer.

Tom> so we can at most allow only a 2-block (well, or 3-block) payload.

We tried turning on multi block payloads and it was a massive disaster.
Many drives reported that they supported 8 block payloads but actually
didn't. Instead of playing the blacklist game we capped it at a single
sector.

Many drives from different vendors were affected by this. So we'd have
to make multi block payloads an explicit opt-in like we did for
discard_zeroes_data. However, given that "big" discards are mainly done
synchronously when creating filesystems, I am not sure there is any real
benefit to this.

-- 
Martin K. Petersen	Oracle Linux Engineering

Thread

[PATCH v5 2/2] Add support for SCT Write Same Shaun Tancheff <shaun@tancheff.com> - 2016-08-10 03:10 +0200
  Re: [PATCH v5 2/2] Add support for SCT Write Same Shaun Tancheff <shaun.tancheff@seagate.com> - 2016-08-10 20:30 +0200
    Re: [PATCH v5 2/2] Add support for SCT Write Same Tom Yan <tom.ty89@gmail.com> - 2016-08-11 10:10 +0200
  Re: [PATCH v5 2/2] Add support for SCT Write Same Tom Yan <tom.ty89@gmail.com> - 2016-08-10 20:40 +0200
    Re: [PATCH v5 2/2] Add support for SCT Write Same "Martin K. Petersen" <martin.petersen@oracle.com> - 2016-08-11 03:50 +0200
      Re: [PATCH v5 2/2] Add support for SCT Write Same Tom Yan <tom.ty89@gmail.com> - 2016-08-11 10:50 +0200
        Re: [PATCH v5 2/2] Add support for SCT Write Same "Martin K. Petersen" <martin.petersen@oracle.com> - 2016-08-12 03:20 +0200
  Re: [PATCH v5 2/2] Add support for SCT Write Same Tom Yan <tom.ty89@gmail.com> - 2016-08-10 20:50 +0200
    Re: [PATCH v5 2/2] Add support for SCT Write Same Tom Yan <tom.ty89@gmail.com> - 2016-08-10 22:20 +0200
      Re: [PATCH v5 2/2] Add support for SCT Write Same Shaun Tancheff <shaun.tancheff@seagate.com> - 2016-08-10 23:30 +0200
        Re: [PATCH v5 2/2] Add support for SCT Write Same "Martin K. Petersen" <martin.petersen@oracle.com> - 2016-08-11 03:40 +0200

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