Sorry for the late comeback, however here are some thoughts. On Fri, Dec 02, 2022 at 06:01:02PM +0900, Tomasz Figa wrote:
On Thu, Nov 24, 2022 at 10:35 PM Hans Verkuil <hverkuil@xxxxxxxxx> wrote:On 21/11/2022 00:44, Michael Grzeschik wrote: > The comments before the vm_map_ram function state that it should be used > for up to 256 KB only, and video buffers are definitely much larger. It > recommends using vmap in that case. > > Signed-off-by: Michael Grzeschik <m.grzeschik@xxxxxxxxxxxxxx> > --- > drivers/media/common/videobuf2/videobuf2-dma-sg.c | 7 ++++--- drivers/media/common/videobuf2/videobuf2-vmalloc.c uses it as well, probably also incorrectly. It makes sense to change that one as well.Comparing vm_map_ram() and vmap(..., VM_MAP, PAGE_KERNEL), for blocks bigger than VMAP_MAX_ALLOC they're equivalent and for smaller blocks the former should be faster, so I don't see what's wrong with the current code.
I got another comment on this from Andrzej Pietrasiewicz where he expands the comment on the use of vmap over vm_map_ram. https://lore.kernel.org/linux-media/64375ff4-dbbb-3d5b-eaf6-32d6780fd496@xxxxxxxxxxxxx As I understand this, we should probably update the vm_map_ram to vmap, due to the expectation that video buffers are long-living objects. Since there are some more places that would probably need to be updated if we should decide to use vmap over vm_map_ram in the whole videbuf2-* users, I would like to clarify on this before making a series. Regards, Michael
> 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/drivers/media/common/videobuf2/videobuf2-dma-sg.c b/drivers/media/common/videobuf2/videobuf2-dma-sg.c > index dcb8de5ab3e84a..e86621fba350f3 100644 > --- a/drivers/media/common/videobuf2/videobuf2-dma-sg.c > +++ b/drivers/media/common/videobuf2/videobuf2-dma-sg.c > @@ -188,7 +188,7 @@ static void vb2_dma_sg_put(void *buf_priv) > dma_unmap_sgtable(buf->dev, sgt, buf->dma_dir, > DMA_ATTR_SKIP_CPU_SYNC); > if (buf->vaddr) > - vm_unmap_ram(buf->vaddr, buf->num_pages); > + vunmap(buf->vaddr); > sg_free_table(buf->dma_sgt); > while (--i >= 0) > __free_page(buf->pages[i]); > @@ -289,7 +289,7 @@ static void vb2_dma_sg_put_userptr(void *buf_priv) > __func__, buf->num_pages); > dma_unmap_sgtable(buf->dev, sgt, buf->dma_dir, DMA_ATTR_SKIP_CPU_SYNC); > if (buf->vaddr) > - vm_unmap_ram(buf->vaddr, buf->num_pages); > + vunmap(buf->vaddr); > sg_free_table(buf->dma_sgt); > if (buf->dma_dir == DMA_FROM_DEVICE || > buf->dma_dir == DMA_BIDIRECTIONAL) > @@ -312,7 +312,8 @@ static void *vb2_dma_sg_vaddr(struct vb2_buffer *vb, void *buf_priv) > ret = dma_buf_vmap(buf->db_attach->dmabuf, &map); > buf->vaddr = ret ? NULL : map.vaddr; > } else { > - buf->vaddr = vm_map_ram(buf->pages, buf->num_pages, -1); > + buf->vaddr = vmap(buf->pages, buf->num_pages, VM_MAP, > + PAGE_KERNEL); > } > } >
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