From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Martin K. Petersen" Subject: Re: [PATCH v5 2/2] Add support for SCT Write Same Date: Wed, 10 Aug 2016 21:47:40 -0400 Message-ID: References: <1470790829-3793-1-git-send-email-shaun@tancheff.com> <1470790829-3793-3-git-send-email-shaun@tancheff.com> Mime-Version: 1.0 Content-Type: text/plain Return-path: Received: from userp1040.oracle.com ([156.151.31.81]:30429 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750857AbcHKBry (ORCPT ); Wed, 10 Aug 2016 21:47:54 -0400 In-Reply-To: (Tom Yan's message of "Wed, 10 Aug 2016 16:50:50 +0000") Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Tom Yan Cc: Shaun Tancheff , Shaun Tancheff , linux-ide@vger.kernel.org, LKML , Christoph Hellwig , Tejun Heo , Josh Bingaman >>>>> "Tom" == Tom Yan 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