linux-kernel - Re: Increased memory usage with scsi-mq

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Message-ID: <3b96a6c9-c5af-c50d-ba02-59863d1ee5f2@redhat.com>
Date:   Wed, 9 Aug 2017 18:50:10 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Christoph Hellwig <hch@....de>
Cc:     "Richard W.M. Jones" <rjones@...hat.com>,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Subject: Re: Increased memory usage with scsi-mq

On 09/08/2017 18:01, Christoph Hellwig wrote:
> On Mon, Aug 07, 2017 at 03:07:48PM +0200, Paolo Bonzini wrote:
>> can_queue should depend on the virtqueue size, which unfortunately can
>> vary for each virtio-scsi device in theory.  The virtqueue size is
>> retrieved by drivers/virtio prior to calling vring_create_virtqueue, and
>> in QEMU it is the second argument to virtio_add_queue.
> 
> Why is that unfortunate?  We don't even have to set can_queue in
> the host template, we can dynamically set it on per-host basis.

Ah, cool, I thought allocations based on can_queue happened already in
scsi_host_alloc, but they happen at scsi_add_host time.

Paolo