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From: Paolo Bonzini <pbonzini@redhat.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Daniel Verkamp <dverkamp@chromium.org>,
	Jens Axboe <axboe@kernel.dk>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	virtualization@lists.linux-foundation.org,
	linux-block@vger.kernel.org,
	Stefan Hajnoczi <stefanha@redhat.com>,
	Changpeng Liu <changpeng.liu@intel.com>
Subject: Re: [PATCH v8] virtio_blk: add discard and write zeroes support
Date: Mon, 29 Oct 2018 19:03:44 +0100	[thread overview]
Message-ID: <bf8fbe85-37a0-be6b-bfd0-da45dfaf7920@redhat.com> (raw)
In-Reply-To: <20181026082640.GA1147@infradead.org>

On 26/10/2018 10:26, Christoph Hellwig wrote:
> On Fri, Oct 26, 2018 at 01:28:54AM +0200, Paolo Bonzini wrote:
>> On 15/10/2018 11:27, Christoph Hellwig wrote:
>>> There is some issues in this spec.  For one using the multiple ranges
>>> also for write zeroes is rather inefficient.  Write zeroes really should
>>> use the same format as read and write.
>>
>> What makes it inefficient?
> 
> We require a memory allocation for each write zeroes instead of encoding
> the lba/len in the command.

Oh, I see.  That's not a spec issue, the lba/length descriptor can be
included in the same buffer as the rest of the command; using
kmalloc_array even for a single-bio REQ_OP_WRITE_ZEROES is a choice made
by this patch, I suppose for simplicity.

It is possible to special case single-bio unmap and write zeroes so that
they don't call virtblk_setup_discard_write_zeroes and avoid
RQF_SPECIAL_PAYLOAD.

Thanks,

Paolo

WARNING: multiple messages have this Message-ID (diff)
From: Paolo Bonzini <pbonzini@redhat.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	virtualization@lists.linux-foundation.org,
	linux-block@vger.kernel.org,
	Stefan Hajnoczi <stefanha@redhat.com>,
	Changpeng Liu <changpeng.liu@intel.com>
Subject: Re: [PATCH v8] virtio_blk: add discard and write zeroes support
Date: Mon, 29 Oct 2018 19:03:44 +0100	[thread overview]
Message-ID: <bf8fbe85-37a0-be6b-bfd0-da45dfaf7920@redhat.com> (raw)
In-Reply-To: <20181026082640.GA1147@infradead.org>

On 26/10/2018 10:26, Christoph Hellwig wrote:
> On Fri, Oct 26, 2018 at 01:28:54AM +0200, Paolo Bonzini wrote:
>> On 15/10/2018 11:27, Christoph Hellwig wrote:
>>> There is some issues in this spec.  For one using the multiple ranges
>>> also for write zeroes is rather inefficient.  Write zeroes really should
>>> use the same format as read and write.
>>
>> What makes it inefficient?
> 
> We require a memory allocation for each write zeroes instead of encoding
> the lba/len in the command.

Oh, I see.  That's not a spec issue, the lba/length descriptor can be
included in the same buffer as the rest of the command; using
kmalloc_array even for a single-bio REQ_OP_WRITE_ZEROES is a choice made
by this patch, I suppose for simplicity.

It is possible to special case single-bio unmap and write zeroes so that
they don't call virtblk_setup_discard_write_zeroes and avoid
RQF_SPECIAL_PAYLOAD.

Thanks,

Paolo

  parent reply	other threads:[~2018-10-29 18:03 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-06  4:19 [PATCH v6] virtio_blk: add DISCARD and WRIET ZEROES commands support Changpeng Liu
2018-06-07 13:10 ` Stefan Hajnoczi
2018-06-07 23:07   ` Liu, Changpeng
2018-06-08 10:20     ` Stefan Hajnoczi
2018-06-11  3:37       ` Liu, Changpeng
2018-06-12 16:05         ` Stefan Hajnoczi
2018-08-28 22:25 ` [PATCH v7] virtio_blk: add discard and write zeroes support Daniel Verkamp
2018-10-12 21:06 ` [PATCH v8] " Daniel Verkamp
2018-10-12 21:06   ` Daniel Verkamp
2018-10-15  0:54   ` Michael S. Tsirkin
2018-10-15  0:54     ` Michael S. Tsirkin
2018-10-15  9:21   ` Ming Lei
2018-10-15  9:27   ` Christoph Hellwig
2018-10-15  9:27     ` Christoph Hellwig
2018-10-15 23:16     ` Daniel Verkamp
2018-10-15 23:16       ` Daniel Verkamp
2018-10-16  1:45       ` Liu, Changpeng
2018-10-16  1:45         ` Liu, Changpeng
2018-10-16  1:40     ` Liu, Changpeng
2018-10-16  1:40       ` Liu, Changpeng
2018-10-25 23:28     ` Paolo Bonzini
2018-10-25 23:28       ` Paolo Bonzini
2018-10-26  8:26       ` Christoph Hellwig
2018-10-26  8:26         ` Christoph Hellwig
2018-10-29  3:21         ` Liu, Changpeng
2018-10-29  3:21           ` Liu, Changpeng
2018-10-29 18:03         ` Paolo Bonzini [this message]
2018-10-29 18:03           ` Paolo Bonzini
2018-10-26  8:08   ` Stefan Hajnoczi
2018-10-26  8:08     ` Stefan Hajnoczi
2018-10-26 14:47     ` Michael S. Tsirkin
2018-10-26 14:47       ` Michael S. Tsirkin
2018-10-29  5:05       ` Stefan Hajnoczi
2018-10-29  5:05         ` Stefan Hajnoczi
2018-11-01 21:25         ` Michael S. Tsirkin
2018-11-01 21:25           ` Michael S. Tsirkin
2018-11-01 22:18           ` Daniel Verkamp
2018-11-01 22:18             ` Daniel Verkamp
2018-11-01 22:40 ` [PATCH v9] " Daniel Verkamp
2018-11-01 22:40   ` Daniel Verkamp
2018-11-01 23:43   ` Dongli Zhang
2018-11-01 23:43     ` Dongli Zhang
2018-11-02 18:25     ` Daniel Verkamp
2018-11-02 18:25       ` Daniel Verkamp
2018-11-02  4:17   ` Stefan Hajnoczi
2018-11-02  4:17     ` Stefan Hajnoczi
2018-12-05  9:46     ` Liu, Changpeng
2018-12-05  9:46       ` Liu, Changpeng
2018-12-05 13:41       ` Michael S. Tsirkin
2018-12-05 13:41         ` Michael S. Tsirkin

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