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From: Leon Romanovsky <leon@kernel.org>
To: Max Gurtovoy <mgurtovoy@nvidia.com>
Cc: mst@redhat.com, virtualization@lists.linux-foundation.org,
	kvm@vger.kernel.org, stefanha@redhat.com, oren@nvidia.com,
	nitzanc@nvidia.com, israelr@nvidia.com, hch@infradead.org,
	linux-block@vger.kernel.org, axboe@kernel.dk
Subject: Re: [PATCH 2/2] virtio-blk: set NUMA affinity for a tagset
Date: Mon, 27 Sep 2021 21:23:28 +0300	[thread overview]
Message-ID: <YVIMIFxjRcfDDub4@unreal> (raw)
In-Reply-To: <0c155679-e1db-3d1e-2b4e-a0f12ce5950c@nvidia.com>

On Mon, Sep 27, 2021 at 08:25:09PM +0300, Max Gurtovoy wrote:
> 
> On 9/27/2021 2:34 PM, Leon Romanovsky wrote:
> > On Sun, Sep 26, 2021 at 05:55:18PM +0300, Max Gurtovoy wrote:
> > > To optimize performance, set the affinity of the block device tagset
> > > according to the virtio device affinity.
> > > 
> > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > ---
> > >   drivers/block/virtio_blk.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > index 9b3bd083b411..1c68c3e0ebf9 100644
> > > --- a/drivers/block/virtio_blk.c
> > > +++ b/drivers/block/virtio_blk.c
> > > @@ -774,7 +774,7 @@ static int virtblk_probe(struct virtio_device *vdev)
> > >   	memset(&vblk->tag_set, 0, sizeof(vblk->tag_set));
> > >   	vblk->tag_set.ops = &virtio_mq_ops;
> > >   	vblk->tag_set.queue_depth = queue_depth;
> > > -	vblk->tag_set.numa_node = NUMA_NO_NODE;
> > > +	vblk->tag_set.numa_node = virtio_dev_to_node(vdev);
> > I afraid that by doing it, you will increase chances to see OOM, because
> > in NUMA_NO_NODE, MM will try allocate memory in whole system, while in
> > the latter mode only on specific NUMA which can be depleted.
> 
> This is a common methodology we use in the block layer and in NVMe subsystem
> and we don't afraid of the OOM issue you raised.

There are many reasons for that, but we are talking about virtio here
and not about NVMe.

> 
> This is not new and I guess that the kernel MM will (or should) be handling
> the fallback you raised.

I afraid that it is not. Can you point me to the place where such
fallback is implemented?

> 
> Anyway, if we're doing this in NVMe I don't see a reason to afraid doing it
> in virtio-blk.

Still, it is nice to have some empirical data to support this copy/paste.

There are too many myths related to optimizations, so finally it will be
good to get some supportive data.

Thanks

  reply	other threads:[~2021-09-27 18:23 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-26 14:55 [PATCH 1/2] virtio: introduce virtio_dev_to_node helper Max Gurtovoy
2021-09-26 14:55 ` [PATCH 2/2] virtio-blk: set NUMA affinity for a tagset Max Gurtovoy
2021-09-27  8:09   ` Stefan Hajnoczi
2021-09-27 17:39     ` Max Gurtovoy
2021-09-28  6:47       ` Stefan Hajnoczi
2021-09-29 15:07         ` Max Gurtovoy
2021-09-30 13:16           ` Stefan Hajnoczi
2021-09-30 13:24             ` Max Gurtovoy
2021-09-27 11:34   ` Leon Romanovsky
2021-09-27 17:25     ` Max Gurtovoy
2021-09-27 18:23       ` Leon Romanovsky [this message]
2021-09-28 15:59         ` Max Gurtovoy
2021-09-28 16:27           ` Leon Romanovsky
2021-09-28 23:28             ` Max Gurtovoy
2021-09-29  6:50               ` Leon Romanovsky
2021-09-29  9:48                 ` Max Gurtovoy
2021-09-27  8:02 ` [PATCH 1/2] virtio: introduce virtio_dev_to_node helper Stefan Hajnoczi
2021-09-27  9:31 ` Michael S. Tsirkin
2021-09-28 16:14   ` Max Gurtovoy

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