From: Stefan Hajnoczi <stefanha@redhat.com>
To: "Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>
Cc: virtio-fs@redhat.com, qemu-devel@nongnu.org, vgoyal@redhat.com,
groug@kaod.org
Subject: Re: [PATCH v3 00/26] virtiofs dax patches
Date: Thu, 6 May 2021 16:37:43 +0100 [thread overview]
Message-ID: <YJQNR2aTvyE5pWqk@stefanha-x1.localdomain> (raw)
In-Reply-To: <20210428110100.27757-1-dgilbert@redhat.com>
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On Wed, Apr 28, 2021 at 12:00:34PM +0100, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
>
> This series adds support for acceleration of virtiofs via DAX
> mapping, using features added in the 5.11 Linux kernel.
>
> DAX originally existed in the kernel for mapping real storage
> devices directly into memory, so that reads/writes turn into
> reads/writes directly mapped into the storage device.
>
> virtiofs's DAX support is similar; a PCI BAR is exposed on the
> virtiofs device corresponding to a DAX 'cache' of a user defined size.
> The guest daemon then requests files to be mapped into that cache;
> when that happens the virtiofsd sends filedescriptors and commands back
> to the QEMU that mmap's those files directly into the memory slot
> exposed to kvm. The guest can then directly read/write to the files
> exposed by virtiofs by reading/writing into the BAR.
>
> A typical invocation would be:
> -device vhost-user-fs-pci,queue-size=1024,chardev=char0,tag=myfs,cache-size=4G
>
> and then the guest must mount with -o dax
>
> Note that the cache doesn't really take VM up on the host, because
> everything placed there is just an mmap of a file, so you can afford
> to use quite a large cache size.
>
> Unlike a real DAX device, the cache is a finite size that's
> potentially smaller than the underlying filesystem (especially when
> mapping granuality is taken into account). Mapping, unmapping and
> remapping must take place to juggle files into the cache if it's too
> small. Some workloads benefit more than others.
>
> Gotchas:
> a) If something else on the host truncates an mmap'd file,
> kvm gets rather upset; for this reason it's advised that DAX is
> currently only suitable for use on non-shared filesystems.
>
> (This series, with a couple of other patches, is at:
> https://gitlab.com/virtio-fs/qemu/-/tree/dgilbert-dax-2021-04-28 )
Overall this looks close but I don't think the FSETID support should be
added to QEMU. Please see my comment on the final patch.
Stefan
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prev parent reply other threads:[~2021-05-06 15:46 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-28 11:00 [PATCH v3 00/26] virtiofs dax patches Dr. David Alan Gilbert (git)
2021-04-28 11:00 ` [PATCH v3 01/26] virtiofs: Fixup printf args Dr. David Alan Gilbert (git)
2021-05-04 14:54 ` Stefan Hajnoczi
2021-05-05 11:06 ` Dr. David Alan Gilbert
2021-05-06 15:56 ` Dr. David Alan Gilbert
2021-04-28 11:00 ` [PATCH v3 02/26] virtiofsd: Don't assume header layout Dr. David Alan Gilbert (git)
2021-05-04 15:12 ` Stefan Hajnoczi
2021-05-06 15:56 ` Dr. David Alan Gilbert
2021-04-28 11:00 ` [PATCH v3 03/26] DAX: vhost-user: Rework slave return values Dr. David Alan Gilbert (git)
2021-05-04 15:23 ` Stefan Hajnoczi
2021-05-27 15:59 ` Dr. David Alan Gilbert
2021-04-28 11:00 ` [PATCH v3 04/26] DAX: libvhost-user: Route slave message payload Dr. David Alan Gilbert (git)
2021-05-04 15:26 ` Stefan Hajnoczi
2021-04-28 11:00 ` [PATCH v3 05/26] DAX: libvhost-user: Allow popping a queue element with bad pointers Dr. David Alan Gilbert (git)
2021-04-28 11:00 ` [PATCH v3 06/26] DAX subprojects/libvhost-user: Add virtio-fs slave types Dr. David Alan Gilbert (git)
2021-04-29 15:48 ` Dr. David Alan Gilbert
2021-04-28 11:00 ` [PATCH v3 07/26] DAX: virtio: Add shared memory capability Dr. David Alan Gilbert (git)
2021-04-28 11:00 ` [PATCH v3 08/26] DAX: virtio-fs: Add cache BAR Dr. David Alan Gilbert (git)
2021-05-05 12:12 ` Stefan Hajnoczi
2021-05-05 18:59 ` Dr. David Alan Gilbert
2021-04-28 11:00 ` [PATCH v3 09/26] DAX: virtio-fs: Add vhost-user slave commands for mapping Dr. David Alan Gilbert (git)
2021-05-05 14:15 ` Stefan Hajnoczi
2021-05-27 16:57 ` Dr. David Alan Gilbert
2021-04-28 11:00 ` [PATCH v3 10/26] DAX: virtio-fs: Fill in " Dr. David Alan Gilbert (git)
2021-05-05 16:43 ` Stefan Hajnoczi
2021-04-28 11:00 ` [PATCH v3 11/26] DAX: virtiofsd Add cache accessor functions Dr. David Alan Gilbert (git)
2021-04-28 11:00 ` [PATCH v3 12/26] DAX: virtiofsd: Add setup/remove mappings fuse commands Dr. David Alan Gilbert (git)
2021-05-06 15:02 ` Stefan Hajnoczi
2021-04-28 11:00 ` [PATCH v3 13/26] DAX: virtiofsd: Add setup/remove mapping handlers to passthrough_ll Dr. David Alan Gilbert (git)
2021-04-28 11:00 ` [PATCH v3 14/26] DAX: virtiofsd: Wire up passthrough_ll's lo_setupmapping Dr. David Alan Gilbert (git)
2021-04-28 11:00 ` [PATCH v3 15/26] DAX: virtiofsd: Make lo_removemapping() work Dr. David Alan Gilbert (git)
2021-04-28 11:00 ` [PATCH v3 16/26] DAX: virtiofsd: route se down to destroy method Dr. David Alan Gilbert (git)
2021-04-28 11:00 ` [PATCH v3 17/26] DAX: virtiofsd: Perform an unmap on destroy Dr. David Alan Gilbert (git)
2021-04-28 11:00 ` [PATCH v3 18/26] DAX/unmap: virtiofsd: Add VHOST_USER_SLAVE_FS_IO Dr. David Alan Gilbert (git)
2021-05-06 15:12 ` Stefan Hajnoczi
2021-05-27 17:44 ` Dr. David Alan Gilbert
2021-05-06 15:16 ` Stefan Hajnoczi
2021-05-27 17:31 ` Dr. David Alan Gilbert
2021-04-28 11:00 ` [PATCH v3 19/26] DAX/unmap virtiofsd: Add wrappers for VHOST_USER_SLAVE_FS_IO Dr. David Alan Gilbert (git)
2021-04-28 12:53 ` Dr. David Alan Gilbert
2021-04-28 11:00 ` [PATCH v3 20/26] DAX/unmap virtiofsd: Parse unmappable elements Dr. David Alan Gilbert (git)
2021-05-06 15:23 ` Stefan Hajnoczi
2021-05-27 17:56 ` Dr. David Alan Gilbert
2021-04-28 11:00 ` [PATCH v3 21/26] DAX/unmap virtiofsd: Route unmappable reads Dr. David Alan Gilbert (git)
2021-05-06 15:27 ` Stefan Hajnoczi
2021-04-28 11:00 ` [PATCH v3 22/26] DAX/unmap virtiofsd: route unmappable write to slave command Dr. David Alan Gilbert (git)
2021-05-06 15:28 ` Stefan Hajnoczi
2021-04-28 11:00 ` [PATCH v3 23/26] DAX:virtiofsd: implement FUSE_INIT map_alignment field Dr. David Alan Gilbert (git)
2021-04-28 11:00 ` [PATCH v3 24/26] vhost-user-fs: Extend VhostUserFSSlaveMsg to pass additional info Dr. David Alan Gilbert (git)
2021-05-06 15:31 ` Stefan Hajnoczi
2021-05-06 15:32 ` Stefan Hajnoczi
2021-04-28 11:00 ` [PATCH v3 25/26] vhost-user-fs: Implement drop CAP_FSETID functionality Dr. David Alan Gilbert (git)
2021-04-28 11:01 ` [PATCH v3 26/26] virtiofsd: Ask qemu to drop CAP_FSETID if client asked for it Dr. David Alan Gilbert (git)
2021-05-06 15:37 ` Stefan Hajnoczi
2021-05-06 16:02 ` Vivek Goyal
2021-05-10 9:05 ` Stefan Hajnoczi
2021-05-10 15:23 ` Vivek Goyal
2021-05-10 15:32 ` Stefan Hajnoczi
2021-05-27 19:09 ` Dr. David Alan Gilbert
2021-06-10 15:29 ` Dr. David Alan Gilbert
2021-06-10 16:23 ` Stefan Hajnoczi
2021-06-16 12:36 ` Dr. David Alan Gilbert
2021-06-16 15:29 ` Stefan Hajnoczi
2021-06-16 18:35 ` Dr. David Alan Gilbert
2021-04-28 11:27 ` [PATCH v3 00/26] virtiofs dax patches no-reply
2021-05-06 15:37 ` Stefan Hajnoczi [this message]
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