[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH v4 07/22] vhost: alloc shareable log
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH v4 07/22] vhost: alloc shareable log |
Date: |
Tue, 22 Sep 2015 14:41:13 +0300 |
On Tue, Sep 22, 2015 at 01:01:03PM +0200, Marc-André Lureau wrote:
> Hi
>
> On Tue, Sep 22, 2015 at 12:12 PM, Michael S. Tsirkin <address@hidden> wrote:
> >> But then it should also VHOST_SET_LOG_BASE all the other devices with
> >> the new log, unless you want to tackle only the future log users. So
> >> it needs to track all the users of the log.
> >
> > We already do this.
> > Same applies to non-memfd->memfd switch.
> >
>
> I failed to see how the log of other devices is being updated when one
> device needs a resize. There are multiple log already in this case.
There's a single log at the moment:
static struct vhost_log *vhost_log;
But all devices are updated by the memory core, we don't
have a list in the vhost code.
> >> Is there a clear benefit
> >> of this? since the memory isn't shared without the memfd passed to
> >> another process and the overhead of memfd is probably quite small, and
> >> pre-shm or future resize will not use the shared memory already.
> >
> > For example, THP doesn't work for memfd at the moment,
> > so all accesses are a bit slower.
>
> What's THP? How is it slower once the fd is mmap?
Transparent huge page. This process doesn't work for
memfd AFAIK.
> > Really, I don't want to merge hacks. Switching from non memfd
> > to memfd but not back has all the signs of one.
> > Let's do it cleanly please.
>
> The current code isn't switching existing logs either. What would be
> simpler to do is to allocate a different log region for the "share"
> case. So there would be no need to switch other non-shareable logs (to
> the cost of using twice the memory needed).
OK, that's not too bad. Let's go for it.
> --
> Marc-André Lureau
- [Qemu-devel] [PATCH v4 04/22] configure: probe for memfd, (continued)
- [Qemu-devel] [PATCH v4 04/22] configure: probe for memfd, marcandre . lureau, 2015/09/19
- [Qemu-devel] [PATCH v4 05/22] util: add linux-only memfd fallback, marcandre . lureau, 2015/09/19
- [Qemu-devel] [PATCH v4 06/22] util: add memfd helpers, marcandre . lureau, 2015/09/19
- [Qemu-devel] [PATCH v4 07/22] vhost: alloc shareable log, marcandre . lureau, 2015/09/19
- Re: [Qemu-devel] [PATCH v4 07/22] vhost: alloc shareable log, Michael S. Tsirkin, 2015/09/21
- Re: [Qemu-devel] [PATCH v4 07/22] vhost: alloc shareable log, Marc-André Lureau, 2015/09/21
- Re: [Qemu-devel] [PATCH v4 07/22] vhost: alloc shareable log, Michael S. Tsirkin, 2015/09/21
- Re: [Qemu-devel] [PATCH v4 07/22] vhost: alloc shareable log, Marc-André Lureau, 2015/09/21
- Re: [Qemu-devel] [PATCH v4 07/22] vhost: alloc shareable log, Michael S. Tsirkin, 2015/09/22
- Re: [Qemu-devel] [PATCH v4 07/22] vhost: alloc shareable log, Marc-André Lureau, 2015/09/22
- Re: [Qemu-devel] [PATCH v4 07/22] vhost: alloc shareable log,
Michael S. Tsirkin <=
- Re: [Qemu-devel] [PATCH v4 07/22] vhost: alloc shareable log, Marc-André Lureau, 2015/09/22
- Re: [Qemu-devel] [PATCH v4 07/22] vhost: alloc shareable log, Michael S. Tsirkin, 2015/09/22
[Qemu-devel] [PATCH v4 08/22] vhost: document log resizing, marcandre . lureau, 2015/09/19
[Qemu-devel] [PATCH v4 09/22] vhost: use a function for each call, marcandre . lureau, 2015/09/19
[Qemu-devel] [PATCH v4 10/22] vhost-user: remove vhost_user_request_translate(), marcandre . lureau, 2015/09/19
[Qemu-devel] [PATCH v4 11/22] vhost-user: send log shm fd along with log_base, marcandre . lureau, 2015/09/19