Hi All,
No reply on the below.
Does anybody came across with the similar issues?
Please let me know if any fixes are already available.
Issues:
1) When free memory pages and CMA free pages are almost equal, min watermark check is failing, resulting in swapping.
2) Almost all the free memory in system is CMA free memory.
3) When ZRAM tries to allocate pages from CMA free areas, the allocation fails.
Please refer below for more details.
Thank you!
Regards,
Pintu
> Date: Tue, 8 Jul 2014 16:41:40 -0700
> From: pintu_agarwal(a)yahoo.com
> Subject: [linux-3.10.17] Could not allocate memory from free CMA areas
> To: linux-mm(a)kvack.org; linux-mm(a)kvack.org; linux-arm-kernel(a)lists.infradead.org; linaro-mm-sig(a)lists.linaro.org
> CC: pintu.k(a)outlook.com; pintu.k(a)samsung.com; vishu_1385(a)yahoo.com; m.szyprowski(a)samsung.com; mina86(a)mina86.com; ngupta(a)vflare.org; iqbalblr(a)gmail.com
>
> Hi,
>
> We are facing one problem on linux 3.10 when we try to use CMA as large as 56MB for 256MB RAM device.
> We found that after certain point of time (during boot), min watermark check is failing when "free_pages" and "free_cma_pages" are almost equal and falls below the min level.
>
> system details:
> ARM embedded device: RAM: 256MB
> Kernel version: 3.10.17
> Fixed Reserved memory: ~40MB
> Available memory: 217MB
> CMA reserved 1 : 56MB
> ZRAM configured: 128MB or 64MB
> min_free_kbytes: 1625 (default)
> Memory controller group enabled (MEMCG)
>
>
> After boot-up the "free -tm" command shows free memory as: ~50MB
> CMA is used for all UI display purposes. CMA used during bootup is close to ~6MB.
> Thus most of the free memory is in the form of CMA free memory.
> ZRAM getting uses was around ~5MB.
>
>
> During boot-up itself we observe that the following conditions are met.
>
>
> if (free_pages - free_cma <= min + lowmem_reserve) {
> printk"[PINTU]: __zone_watermark_ok: failed !\n");
>
> return false;
> }
> Here: free_pages was: 12940, free_cma was: 12380, min: 566, lowmem: 0
>
>
> Thus is condition is met most of the time.
> And because of this watermark failure, Kswapd is waking up frequently.
> The /proc/pagetypeinfo reports that most of the higher order pages are from CMA regions.
>
>
> We also observed that ZRAM is trying to allocate memory from CMA region and failing.
>
> We also tried by decreasing the CMA region to 20MB. With this the watermark failure is not happening in boot time. But if we launch more than 3 apps {Browser, music-player etc}, again the watermark started failing.
>
> Also we tried decreasing the min_free_kbytes=256, and with this also watermark is passed.
>
> Our observation is that ZRAM/zsmalloc trying to allocate memory from CMA areas and failed.
>
>
> Please let us know if anybody have come across the same problem and how to resolve this issue.
>
>
>
>
>
> Thank You!
> Regards,
> Pintu
On Tue, Mar 25, 2014 at 07:01:10PM +0100, Sam Ravnborg wrote:
> >
> > There are two things that don't work too well with this. First this
> > causes the build to break if the build machine doesn't have the new
> > public header (include/uapi/linux/dma-buf.h) installed yet. So the only
> > way to make this work would be by building the kernel once with SAMPLES
> > disabled, install the headers and then build again with SAMPLES enabled.
> > Which really isn't very nice.
> >
> > One other option that I've tried is to modify the include path so that
> > the test program would get the in-tree copy of the public header file,
> > but that didn't build properly either because the header files aren't
> > properly sanitized and therefore the compiler complains about it
> > (include/uapi/linux/types.h).
> >
> > One other disadvantage of carrying the sample program in the tree is
> > that there's only infrastructure to build programs natively on the build
> > machine. That's somewhat unfortunate because if you want to run the test
> > program on a different architecture you have to either compile the
> > kernel natively on that architecture (which isn't very practical on many
> > embedded devices) or cross-compile manually.
> >
> > I think a much nicer solution would be to add infrastructure to cross-
> > compile these test programs, so that they end up being built for the
> > same architecture as the kernel image (i.e. using CROSS_COMPILE).
> >
> > Adding Michal and the linux-kbuild mailing list, perhaps this has been
> > discussed before, or maybe somebody has a better idea on how to solve
> > this.
> I actually looked into this some time ago.
> May try to dust off the patch.
> IIRC the kernel provided headers were used for building - not the one installed on the machine.
> And crosscompile were supported.
That sounds exactly like what I'd want for this. If you need any help,
please let me know.
Thanks,
Thierry
So after some more hacking I've moved dma-buf to its own subdirectory,
drivers/dma-buf and applied the fence patches to its new place. I believe that the
first patch should be applied regardless, and the rest should be ready now.
:-)
Changes to the fence api:
- release_fence -> fence_release etc.
- __fence_init -> fence_init
- __fence_signal -> fence_signal_locked
- __fence_is_signaled -> fence_is_signaled_locked
- Changing BUG_ON to WARN_ON in fence_later, and return NULL if it triggers.
Android can expose fences to userspace. It's possible to make the new fence
mechanism expose the same fences to userspace by changing sync_fence_create
to take a struct fence instead of a struct sync_pt. No other change is needed,
because only the fence parts of struct sync_pt are used. But because the
userspace fences are a separate problem and I haven't really looked at it yet
I feel it should stay in staging, for now.
---
Maarten Lankhorst (9):
dma-buf: move to drivers/dma-buf
fence: dma-buf cross-device synchronization (v18)
seqno-fence: Hardware dma-buf implementation of fencing (v6)
dma-buf: use reservation objects
android: convert sync to fence api, v6
reservation: add support for fences to enable cross-device synchronisation
dma-buf: add poll support, v3
reservation: update api and add some helpers
reservation: add suppport for read-only access using rcu
Documentation/DocBook/device-drivers.tmpl | 8
MAINTAINERS | 4
drivers/Makefile | 1
drivers/base/Kconfig | 9
drivers/base/Makefile | 1
drivers/base/dma-buf.c | 743 --------------------
drivers/base/reservation.c | 39 -
drivers/dma-buf/Makefile | 1
drivers/dma-buf/dma-buf.c | 907 ++++++++++++++++++++++++
drivers/dma-buf/fence.c | 431 +++++++++++
drivers/dma-buf/reservation.c | 477 +++++++++++++
drivers/dma-buf/seqno-fence.c | 73 ++
drivers/gpu/drm/armada/armada_gem.c | 2
drivers/gpu/drm/drm_prime.c | 8
drivers/gpu/drm/exynos/exynos_drm_dmabuf.c | 2
drivers/gpu/drm/i915/i915_gem_dmabuf.c | 3
drivers/gpu/drm/nouveau/nouveau_drm.c | 1
drivers/gpu/drm/nouveau/nouveau_gem.h | 1
drivers/gpu/drm/nouveau/nouveau_prime.c | 7
drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c | 2
drivers/gpu/drm/radeon/radeon_drv.c | 2
drivers/gpu/drm/radeon/radeon_prime.c | 8
drivers/gpu/drm/tegra/gem.c | 2
drivers/gpu/drm/ttm/ttm_object.c | 2
drivers/media/v4l2-core/videobuf2-dma-contig.c | 2
drivers/staging/android/Kconfig | 1
drivers/staging/android/Makefile | 2
drivers/staging/android/ion/ion.c | 3
drivers/staging/android/sw_sync.c | 6
drivers/staging/android/sync.c | 913 ++++++++----------------
drivers/staging/android/sync.h | 79 +-
drivers/staging/android/sync_debug.c | 247 ++++++
drivers/staging/android/trace/sync.h | 12
include/drm/drmP.h | 3
include/linux/dma-buf.h | 21 -
include/linux/fence.h | 360 +++++++++
include/linux/reservation.h | 82 ++
include/linux/seqno-fence.h | 116 +++
include/trace/events/fence.h | 128 +++
39 files changed, 3258 insertions(+), 1451 deletions(-)
delete mode 100644 drivers/base/dma-buf.c
delete mode 100644 drivers/base/reservation.c
create mode 100644 drivers/dma-buf/Makefile
create mode 100644 drivers/dma-buf/dma-buf.c
create mode 100644 drivers/dma-buf/fence.c
create mode 100644 drivers/dma-buf/reservation.c
create mode 100644 drivers/dma-buf/seqno-fence.c
create mode 100644 drivers/staging/android/sync_debug.c
create mode 100644 include/linux/fence.h
create mode 100644 include/linux/seqno-fence.h
create mode 100644 include/trace/events/fence.h
--
Signature
Hello,
This is one more respin of the patches which add support for creating
reserved memory regions defined in device tree. The last attempt
(http://lists.linaro.org/pipermail/linaro-mm-sig/2014-February/003738.html)
ended in merging only half of the code, so right now we have complete
documentation merged and only basic code, which implements a half of it
is written in the documentation. Although the merged patches allow to
reserve memory, there is no way of using it for devices and drivers.
This situation makes CMA rather useless, as the main architecture (ARM),
which used it, has been converted from board-file based system
initialization to device tree. Thus there is no place to use direct
calls to dma_declare_contiguous() and some new solution, which bases on
device tree, is urgently needed.
This patch series fixes this issue. It provides two, already widely
discussed and already present in the kernel, drivers for reserved
memory: first based on DMA-coherent allocator, second using Contiguous
Memory Allocator. The first one nicely implements typical 'carved out'
reserved memory way of allocating contiguous buffers in a kernel-style
way. The memory is used exclusively by devices assigned to the given
memory region. The second one allows to reuse reserved memory for
movable kernel pages (like disk buffers, anonymous memory) and migrates
it out when device to allocates contiguous memory buffer. Both driver
provides memory buffers via standard dma-mapping API.
The patches have been rebased on top of latest CMA and mm changes merged
to akmp kernel tree.
To define a 64MiB CMA region following node is needed:
multimedia_reserved: multimedia_mem_region {
compatible = "shared-dma-pool";
reusable;
size = <0x4000000>;
alignment = <0x400000>;
};
Similarly, one can define 64MiB region with DMA coherent memory:
multimedia_reserved: multimedia_mem_region {
compatible = "shared-dma-pool";
no-map;
size = <0x4000000>;
alignment = <0x400000>;
};
Then the defined region can be assigned to devices:
scaler: scaler@12500000 {
memory-region = <&multimedia_reserved>;
/* ... */
};
codec: codec@12600000 {
memory-region = <&multimedia_reserved>;
/* ... */
};
Best regards
Marek Szyprowski
Samsung R&D Institute Poland
Changes since the version posted in '[PATCH v6 00/11] reserved-memory
regions/CMA in devicetree, again' thread
http://lists.linaro.org/pipermail/linaro-mm-sig/2014-February/003738.html:
- rebased on top of '[PATCH v3 -next 0/9] CMA: generalize CMA reserved
area management code' patch series on v3.16-rc3
- improved dma-coherent driver, now it correctly handles assigning more
than one device to the given memory region
Patch summary:
Marek Szyprowski (4):
drivers: of: add automated assignment of reserved regions to client
devices
drivers: of: initialize and assign reserved memory to newly created
devices
drivers: dma-coherent: add initialization from device tree
drivers: dma-contiguous: add initialization from device tree
drivers/base/dma-coherent.c | 137 ++++++++++++++++++++++++++++++++++------
drivers/base/dma-contiguous.c | 67 ++++++++++++++++++++
drivers/of/of_reserved_mem.c | 70 ++++++++++++++++++++
drivers/of/platform.c | 7 ++
include/linux/cma.h | 3 +
include/linux/of_reserved_mem.h | 7 ++
mm/cma.c | 69 +++++++++++++++-----
7 files changed, 324 insertions(+), 36 deletions(-)
--
1.9.2
Hello,
I am trying to read a DMA buff ,allocated and manged by driver "A".
reader is a different driver "B" (which simply make DMA buffer accessible
by /proc to user space).
Can dmabuf APIs can be used for all reader and writer synchronization
issues ?
I want to use dmabuf between two drivers , do i need to go to user space
and use "fd" to get struct dma_buf * from dma_buf_get(int fd).
there is any way to use dmabuf APIs in kernel space only (between two
drivers ) without going to user space ?
example code will certainly help.
--
Regards
Rahul Dargainya
On Mon, 9 Jun 2014 14:06:33 +0300
Pekka Paalanen <pekka.paalanen(a)collabora.co.uk> wrote:
> On Mon, 9 Jun 2014 11:00:04 +0200
> Benjamin Gaignard <benjamin.gaignard(a)linaro.org> wrote:
>
> > On my hardware the patches you have (+ this one on gstwaylandsink
> > https://bugzilla.gnome.org/show_bug.cgi?id=711155) allow me to do zero
> > copy between the hardware video decoder and the display engine. I
> > don't have implemented GPU yet because my hardware is able to do
> > compose few video overlays planes and it was enough for my tests.
>
> Right.
>
> What I have been thinking is, that the compositor must be able to use
> the new wl_buffer and we need to guarantee that before-hand. If the
> compositor fails to use a wl_buffer when the client has already
> attached it to a wl_surface and it is time to repaint, it is too late
> and the user will see a glitch. Recovering from that requires asking
> the client to provide a new wl_buffer of a different kind, which might
> take time. Or a very rude compositor would just send a protocol error,
> and then we'd get bug reports like "the video player just disappears
> when I try to play (and ps. I have an old kernel that doesn't support
> importing whatever)".
>
> I believe we must allow the compositor to test the wl_buffer before it
> is usable for the client. That is the reason for the roundtrippy design
> of the below proposal.
>
> Because we do not even try to communicate all the possible restrictions
> to the client for it to match, we can leave the validation strictly as
> a kernel internal issue. Buffer migration inside the kernel might even
> magically solve some of the mismatches. It does leave the problem of
> what can the client do, if it doesn't fill all the requirements for the
> compositor to be able to import the dmabufs. But what restrictions
> other than color format we can or should communicate, and where does
> user space get them in the first place... *hand-waving*
>
> But, this also leaves it up to the compositor to choose how/where it
> wants to import the dmabufs. If a compositor is usually compositing
> with GL, it will try to import with EGL on whatever GPU it is using. If
> the compositor uses a software renderer, it can try to mmap the dmabufs
> (or try this as a fallback, if the EGL import fails). If the compositor
> is absolutely sure it can rely on the hardware display engine to
> composite these buffers (note, buffers! You don't know to which
> surfaces these buffers will be attached to), it can import directly
> with DRM as FB objects, or V4L, or whatever. A compositor with the
> fullscreen shell extension but without the sub-surface extension comes
> to mind.
>
> In summary, the compositor must be able to use the wl_buffer in its
> default/fallback compositing path. If the wl_buffer is also suitable
> for direct scanout, e.g. on an overlay, that is "just" a bonus.
>
> With the round-trippy design, I am assuming that you can
> export-pass-import a set of dmabufs once, and then reuse them as long
> as you don't need to e.g. resize them. Is this a reasonable assumption?
> Are there any, for instance, hardware video decoders that just insist on
> exporting a new buffer for every frame?
>
> I am tracking the proposal in
> http://cgit.collabora.com/git/user/pq/weston.git/log/?h=linux_dmabuf
>
> So far I added back the event to advertise the supported
> drm_fourcc formats, since that is probably quite crucial.
Yeah, about that...
https://www.khronos.org/registry/egl/extensions/EXT/EGL_EXT_image_dma_buf_i…
provides no way for the compositor to query, what formats the EGL
implementation might support for importing dmabufs. I'm not sure GBM
has that yet either.
So there is no way a compositor could advertise the set of supported
formats, since it has no way of knowing, has it?
Any suggested solutions for this? Or would probing (export dmabuf, send
to compositor, wait for compositor to ack/reject) for suitable formats
be enough?
Thanks,
pq
> > 2014-06-06 17:30 GMT+02:00 Pekka Paalanen <pekka.paalanen(a)collabora.co.uk>:
> > > Hi,
> > >
> > > the previous attempt at introducing a generic wl_dmabuf protocol to
> > > Wayland didn't end too well:
> > > http://lists.freedesktop.org/archives/wayland-devel/2013-December/012390.ht…
> > > http://lists.freedesktop.org/archives/wayland-devel/2013-December/012455.ht…
> > > http://lists.freedesktop.org/archives/wayland-devel/2013-December/012566.ht…
> > > http://lists.freedesktop.org/archives/wayland-devel/2014-January/012727.html
> > >
> > > We are again interested in this, and I did a quick Friday evening draft
> > > to open the discussion again. The base of the draft was a quick look at
> > > https://www.khronos.org/registry/egl/extensions/EXT/EGL_EXT_image_dma_buf_i…
> > >
> > > The basic idea is, that a client has one or more dmabufs it wants to
> > > share with the compositor, making up a single logical buffer (a single
> > > image). The client chooses where and how to export those dmabufs. The
> > > dmabuf fds and metadata are sent to the compositor, the compositor
> > > assembles and tries to import them. If the import succeeds, a wl_buffer
> > > object is created. If the import fails, the client is notified that the
> > > compositor can't use these, it would be better to try something else.
> > >
> > > I assume that if the "import" succeeds, the compositor is able to use
> > > the buffers, e.g. at least turn them into a GL-texture or mmap them, if
> > > not also able to scan out or put on a hw overlay. This could be any kind
> > > of checking to verify that the buffers are usable. Finding out that it
> > > won't work after the client is already using the wl_buffer must not
> > > happen, as we have no way to recover from it: the client will get
> > > disconnected. So the point is knowing in advance, that the buffers are
> > > usable on both sides, preferrably before the client has filled them with
> > > data, but I suppose in the usual case the buffer is already filled.
> > >
> > > As creating a dmabuf-based wl_buffer requires a roundtrip in this
> > > scheme, I assume it only needs to be done rarely, and the same buffer
> > > can be re-used many times with proper synchronization.
> > >
> > > The crude draft is below. Some questions:
> > > - Does this sound sane to you?
> > > - What other metadata would we need? Thierry had some issues with
> > > tiling formats I think.
> > > - This "check if the dmabuf is really usable" is needed, right? We
> > > can't just assume that any dmabuf will work?
> > > - Do we need anything for fences here, or is the dmabuf fd enough?
> > > - Does someone already have something similar running?
On Mon, Jun 9, 2014 at 8:44 AM, Pekka Paalanen
<pekka.paalanen(a)collabora.co.uk> wrote:
> On Mon, 9 Jun 2014 12:23:18 +0100
> Daniel Stone <daniel(a)fooishbar.org> wrote:
>
>> Hi,
>>
>> On 9 June 2014 12:06, Pekka Paalanen <pekka.paalanen(a)collabora.co.uk> wrote:
>>
>> > On Mon, 9 Jun 2014 11:00:04 +0200
>> > Benjamin Gaignard <benjamin.gaignard(a)linaro.org> wrote:
>> > > One of the main comment on the latest patches was that wl_dmabuf use
>> > > DRM for buffer allocation.
>> > > This appear to be an issue since wayland doesn't want to rely on one
>> > > specific framework (DRM, or V4L2) for buffer allocation, so we have
>> > > start working on a "central dmabuf allocation" on kernel side. The
>> > > goal is provide some as generic as possible to make it acceptable by
>> > > wayland.
>> >
>> > Why would Wayland need a central allocator for dmabuf?
>> >
>>
>> I think you've just answered your own question further below:
>>
>>
>> > > On my hardware the patches you have (+ this one on gstwaylandsink
>> > > https://bugzilla.gnome.org/show_bug.cgi?id=711155) allow me to do zero
>> > > copy between the hardware video decoder and the display engine. I
>> > > don't have implemented GPU yet because my hardware is able to do
>> > > compose few video overlays planes and it was enough for my tests.
>> >
>> > Right.
>> >
>> > What I have been thinking is, that the compositor must be able to use
>> > the new wl_buffer and we need to guarantee that before-hand. If the
>> > compositor fails to use a wl_buffer when the client has already
>> > attached it to a wl_surface and it is time to repaint, it is too late
>> > and the user will see a glitch. Recovering from that requires asking
>> > the client to provide a new wl_buffer of a different kind, which might
>> > take time. Or a very rude compositor would just send a protocol error,
>> > and then we'd get bug reports like "the video player just disappears
>> > when I try to play (and ps. I have an old kernel that doesn't support
>> > importing whatever)".
>> >
>> > I believe we must allow the compositor to test the wl_buffer before it
>> > is usable for the client. That is the reason for the roundtrippy design
>> > of the below proposal.
>> >
>>
>> A central allocator would solve these issues, by having everyone agree on
>> the restrictions upfront, instead of working out which of the media decode
>> engine, camera, GPU, or display controller is the lowest common
>> denominator, and forcing all allocations through there.
>>
>> One such solution was discussed a while back WRT ION:
>> https://lwn.net/Articles/565469/
>>
>> See the 'possible solutions' part for a way for people to agree on
>> restrictions wrt tiling, stride, contiguousness, etc.
>
> Hi,
>
> that's an excellent article. I didn't know that delayed allocation of
> dmabufs was not even possible yet, which would have allowed us to
> not think about importing failures and simply let the client fall back
> with "ok, don't use dmabuf with this particular device then".
hrm? I know of at least a couple drm drivers that defer allocation of
backing pages..
> What is the conclusion here?
>
> Wayland protocol does not need to consider import failures at all, and
> can simply punt those as protocol errors, which essentially kill the app
> if they ever happen?
>
> Do we need to wait for the central allocator in kernel to materialize
> before we can design the protocol? Is it simply too early to try to do
> it now?
I do tend to think the ION/central-allocator is just substituting one
problem for another. It doesn't really solve the problem of how
different devices which don't actually know each other can decide on
buffers that they can share. On an phone/tablet/etc you know up front
when building the kernel what devices there are and in what uses-cases
they will be used, etc. But that isn't really solving the more
general case.
> Was the idea of dmabuf in-kernel constraint negotiation with delayed
> allocation rejected in favour of a central allocator?
not really, that I know of. I still think we need to spiff out
dma-mapping to better handle placement constraints. (Although still
prefer format constraints to be a userspace topic.)
pengutronix is doing some work in this area:
http://elinux.org/images/b/b0/OSELAS.Presentation-DMABUF-migration.pdf
BR,
-R
> Will Intel, Nouveau and Radeon support the central allocator, or will
> it remain for ARM-related devices only?
>
>
> Thanks,
> pq
On 06/09/2014 01:23 PM, Daniel Stone wrote:
> Hi,
>
> On 9 June 2014 12:06, Pekka Paalanen <pekka.paalanen(a)collabora.co.uk
> <mailto:pekka.paalanen@collabora.co.uk>> wrote:
>
> On Mon, 9 Jun 2014 11:00:04 +0200
> Benjamin Gaignard <benjamin.gaignard(a)linaro.org
> <mailto:benjamin.gaignard@linaro.org>> wrote:
> > One of the main comment on the latest patches was that wl_dmabuf use
> > DRM for buffer allocation.
> > This appear to be an issue since wayland doesn't want to rely on one
> > specific framework (DRM, or V4L2) for buffer allocation, so we have
> > start working on a "central dmabuf allocation" on kernel side. The
> > goal is provide some as generic as possible to make it acceptable by
> > wayland.
>
> Why would Wayland need a central allocator for dmabuf?
>
>
> I think you've just answered your own question further below:
>
>
> > On my hardware the patches you have (+ this one on gstwaylandsink
> > https://bugzilla.gnome.org/show_bug.cgi?id=711155
> <https://urldefense.proofpoint.com/v1/url?u=https://bugzilla.gnome.org/show_…>)
> allow me to do zero
> > copy between the hardware video decoder and the display engine. I
> > don't have implemented GPU yet because my hardware is able to do
> > compose few video overlays planes and it was enough for my tests.
>
> Right.
>
> What I have been thinking is, that the compositor must be able to use
> the new wl_buffer and we need to guarantee that before-hand. If the
> compositor fails to use a wl_buffer when the client has already
> attached it to a wl_surface and it is time to repaint, it is too late
> and the user will see a glitch. Recovering from that requires asking
> the client to provide a new wl_buffer of a different kind, which might
> take time. Or a very rude compositor would just send a protocol error,
> and then we'd get bug reports like "the video player just disappears
> when I try to play (and ps. I have an old kernel that doesn't support
> importing whatever)".
>
> I believe we must allow the compositor to test the wl_buffer before it
> is usable for the client. That is the reason for the roundtrippy
> design
> of the below proposal.
>
>
> A central allocator would solve these issues, by having everyone agree
> on the restrictions upfront, instead of working out which of the media
> decode engine, camera, GPU, or display controller is the lowest common
> denominator, and forcing all allocations through there.
>
> One such solution was discussed a while back WRT ION:
> https://lwn.net/Articles/565469/
> <https://urldefense.proofpoint.com/v1/url?u=https://lwn.net/Articles/565469/…>
>
> See the 'possible solutions' part for a way for people to agree on
> restrictions wrt tiling, stride, contiguousness, etc.
Hi!
I think before deciding on something like this, one needs also to
account for the virtual drivers like vmwgfx.
Here, a dma-buf internally holds an opaque handle to an object on the
host / hypervisor, and the actual memory buffer is only temporarily
allocated for dma-buf operations that strictly need it. Not to hold the
data while transferring it between devices or applications.
Let's say you'd want to use a USB display controller in a virtual
machine with the vmwgfx exported prime objects, for example. There's no
common denominator. The vmwgfx driver would need to read the dma-buf
data from the host object at sg-table export (dma-buf map) time.
Whereas if you just want to share data between a wayland server and
client, no pages are ever allocated and the only thing passed
around is in effect the opaque handle to the host / hypervisor object.
I'm currently having trouble seeing how a central allocator would be
able to deal with this?
/Thomas
>
> Cheers,
> Daniel
>
>
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