on 2024/7/10 22:48, Christian König wrote:
Am 10.07.24 um 16:35 schrieb Lei Liu:
on 2024/7/10 22:14, Christian König wrote:
Am 10.07.24 um 15:57 schrieb Lei Liu:
Use vm_insert_page to establish a mapping for the memory allocated
by dmabuf, thus supporting direct I/O read and write; and fix the
issue of incorrect memory statistics after mapping dmabuf memory.
Well big NAK to that! Direct I/O is intentionally disabled on DMA-bufs.
Hello! Could you explain why direct_io is disabled on DMABUF? Is
there any historical reason for this?
It's basically one of the most fundamental design decision of DMA-Buf.
The attachment/map/fence model DMA-buf uses is not really compatible
with direct I/O on the underlying pages.
Thank you! Is there any related documentation on this? I would like to
understand and learn more about the fundamental reasons for the lack of
support.
We already discussed enforcing that in the DMA-buf framework and
this patch probably means that we should really do that.
Regards,
Christian.
Thank you for your response. With the application of AI large model
edgeification, we urgently need support for direct_io on DMABUF to
read some very large files. Do you have any new solutions or plans
for this?
We have seen similar projects over the years and all of those turned
out to be complete shipwrecks.
There is currently a patch set under discussion to give the network
subsystem DMA-buf support. If you are interest in network direct I/O
that could help.
Is there a related introduction link for this patch?
Additional to that a lot of GPU drivers support userptr usages, e.g.
to import malloced memory into the GPU driver. You can then also do
direct I/O on that malloced memory and the kernel will enforce correct
handling with the GPU driver through MMU notifiers.
But as far as I know a general DMA-buf based solution isn't possible.
1.The reason we need to use DMABUF memory here is that we need to share
memory between the CPU and APU. Currently, only DMABUF memory is
suitable for this purpose. Additionally, we need to read very large files.
2. Are there any other solutions for this? Also, do you have any plans
to support direct_io for DMABUF memory in the future?
Regards,
Christian.
Regards,
Lei Liu.
Lei Liu (2):
mm: dmabuf_direct_io: Support direct_io for memory allocated by
dmabuf
mm: dmabuf_direct_io: Fix memory statistics error for dmabuf
allocated
memory with direct_io support
drivers/dma-buf/heaps/system_heap.c | 5 +++--
fs/proc/task_mmu.c | 8 +++++++-
include/linux/mm.h | 1 +
mm/memory.c | 15 ++++++++++-----
mm/rmap.c | 9 +++++----
5 files changed, 26 insertions(+), 12 deletions(-)
