From: "Michael S. Tsirkin" <mst@redhat.com>
To: Jason Wang <jasowang@redhat.com>
Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
peterx@redhat.com, linux-mm@kvack.org, aarcange@redhat.com
Subject: Re: [RFC PATCH V2 5/5] vhost: access vq metadata through kernel virtual address
Date: Thu, 7 Mar 2019 10:34:39 -0500 [thread overview]
Message-ID: <20190307101708-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <15105894-4ec1-1ed0-1976-7b68ed9eeeda@redhat.com>
On Thu, Mar 07, 2019 at 10:45:57AM +0800, Jason Wang wrote:
>
> On 2019/3/7 上午12:31, Michael S. Tsirkin wrote:
> > > +static void vhost_set_vmap_dirty(struct vhost_vmap *used)
> > > +{
> > > + int i;
> > > +
> > > + for (i = 0; i < used->npages; i++)
> > > + set_page_dirty_lock(used->pages[i]);
> > This seems to rely on page lock to mark page dirty.
> >
> > Could it happen that page writeback will check the
> > page, find it clean, and then you mark it dirty and then
> > invalidate callback is called?
> >
> >
>
> Yes. But does this break anything?
> The page is still there, we just remove a
> kernel mapping to it.
>
> Thanks
Yes it's the same problem as e.g. RDMA:
we've just marked the page as dirty without having buffers.
Eventually writeback will find it and filesystem will complain...
So if the pages are backed by a non-RAM-based filesystem, it’s all just broken.
one can hope that RDMA guys will fix it in some way eventually.
For now, maybe add a flag in e.g. VMA that says that there's no
writeback so it's safe to mark page dirty at any point?
--
MST
next prev parent reply other threads:[~2019-03-07 15:34 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-06 7:18 [RFC PATCH V2 0/5] vhost: accelerate metadata access through vmap() Jason Wang
2019-03-06 7:18 ` [RFC PATCH V2 1/5] vhost: generalize adding used elem Jason Wang
2019-03-06 7:18 ` [RFC PATCH V2 2/5] vhost: fine grain userspace memory accessors Jason Wang
2019-03-06 10:45 ` Christophe de Dinechin
2019-03-07 2:38 ` Jason Wang
2019-03-06 7:18 ` [RFC PATCH V2 3/5] vhost: rename vq_iotlb_prefetch() to vq_meta_prefetch() Jason Wang
2019-03-06 7:18 ` [RFC PATCH V2 4/5] vhost: introduce helpers to get the size of metadata area Jason Wang
2019-03-06 10:56 ` Christophe de Dinechin
2019-03-07 2:40 ` Jason Wang
2019-03-06 18:43 ` Souptick Joarder
2019-03-07 2:42 ` Jason Wang
2019-03-06 7:18 ` [RFC PATCH V2 5/5] vhost: access vq metadata through kernel virtual address Jason Wang
2019-03-06 16:31 ` Michael S. Tsirkin
2019-03-07 2:45 ` Jason Wang
2019-03-07 15:34 ` Michael S. Tsirkin [this message]
2019-03-07 19:09 ` Jerome Glisse
2019-03-07 19:38 ` Andrea Arcangeli
2019-03-07 20:17 ` Jerome Glisse
2019-03-07 21:27 ` Andrea Arcangeli
2019-03-08 9:13 ` Jason Wang
2019-03-08 19:11 ` Andrea Arcangeli
2019-03-11 7:21 ` Jason Wang
2019-03-11 14:45 ` Jan Kara
2019-03-08 8:31 ` Jason Wang
2019-03-07 15:47 ` Michael S. Tsirkin
2019-03-07 17:56 ` Michael S. Tsirkin
2019-03-07 19:16 ` Andrea Arcangeli
2019-03-08 8:50 ` Jason Wang
2019-03-08 14:58 ` Jerome Glisse
2019-03-11 7:18 ` Jason Wang
2019-03-08 19:48 ` Andrea Arcangeli
2019-03-08 20:06 ` Jerome Glisse
2019-03-11 7:40 ` Jason Wang
2019-03-11 12:48 ` Michael S. Tsirkin
2019-03-11 13:43 ` Andrea Arcangeli
2019-03-12 2:56 ` Jason Wang
2019-03-12 3:51 ` Michael S. Tsirkin
2019-03-12 2:52 ` Jason Wang
2019-03-12 3:50 ` Michael S. Tsirkin
2019-03-12 7:15 ` Jason Wang
2019-03-07 19:17 ` Jerome Glisse
2019-03-08 2:21 ` Michael S. Tsirkin
2019-03-08 2:55 ` Jerome Glisse
2019-03-08 3:16 ` Michael S. Tsirkin
2019-03-08 3:40 ` Jerome Glisse
2019-03-08 3:43 ` Michael S. Tsirkin
2019-03-08 3:45 ` Jerome Glisse
2019-03-08 9:15 ` Jason Wang
2019-03-08 8:58 ` Jason Wang
2019-03-08 12:56 ` Michael S. Tsirkin
2019-03-08 15:02 ` Jerome Glisse
2019-03-08 19:13 ` Andrea Arcangeli
2019-03-08 14:12 ` [RFC PATCH V2 0/5] vhost: accelerate metadata access through vmap() Christoph Hellwig
2019-03-11 7:13 ` Jason Wang
2019-03-11 13:59 ` Michael S. Tsirkin
2019-03-11 18:14 ` David Miller
2019-03-12 2:59 ` Jason Wang
2019-03-12 3:52 ` Michael S. Tsirkin
2019-03-12 7:17 ` Jason Wang
2019-03-12 11:54 ` Michael S. Tsirkin
2019-03-12 15:46 ` James Bottomley
2019-03-12 20:04 ` Andrea Arcangeli
2019-03-12 20:53 ` James Bottomley
2019-03-12 21:11 ` Andrea Arcangeli
2019-03-12 21:19 ` James Bottomley
2019-03-12 21:53 ` Andrea Arcangeli
2019-03-12 22:02 ` James Bottomley
2019-03-12 22:50 ` Andrea Arcangeli
2019-03-12 22:57 ` James Bottomley
2019-03-13 16:05 ` Christoph Hellwig
2019-03-13 16:37 ` James Bottomley
2019-03-14 10:42 ` Michael S. Tsirkin
2019-03-14 13:49 ` Jason Wang
2019-03-14 19:33 ` Andrea Arcangeli
2019-03-15 4:39 ` Jason Wang
2019-03-12 5:14 ` James Bottomley
2019-03-12 7:51 ` Jason Wang
2019-03-12 7:53 ` Jason Wang
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