2023-07-19 13:50:31

by Sumitra Sharma

Subject: [PATCH] Remove unnecessary calls to kmap{,_local_page}() when acquiring pages using GFP_DMA32.

The GFP_DMA32 uses the DMA32 zone to satisfy the allocation
requests. Therefore, pages allocated with GFP_DMA32 cannot
come from Highmem.

Avoid using calls to kmap() / kunmap() as the kmap() is being
deprecated [1].

Avoid using calls to kmap_local_page() / kunmap_local() as the
code does not depends on the implicit disable of migration of
local mappings and is, in fact, an unnecessary overhead for
the main code [2].

Hence, use a plain page_address() directly in the
psb_mmu_alloc_pd function.

[1]: https://lore.kernel.org/all/[email protected]/
[2]: https://lwn.net/Articles/836503/

Suggested-by: Ira Weiny <[email protected]>
Signed-off-by: Sumitra Sharma <[email protected]>
---
drivers/gpu/drm/gma500/mmu.c | 11 +++--------
1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/gma500/mmu.c b/drivers/gpu/drm/gma500/mmu.c
index a70b01ccdf70..1a44dd062fd1 100644
--- a/drivers/gpu/drm/gma500/mmu.c
+++ b/drivers/gpu/drm/gma500/mmu.c
@@ -184,20 +184,15 @@ struct psb_mmu_pd *psb_mmu_alloc_pd(struct psb_mmu_driver *driver,
pd->invalid_pte = 0;
}

- v = kmap_local_page(pd->dummy_pt);
+ v = page_address(pd->dummy_pt);
for (i = 0; i < (PAGE_SIZE / sizeof(uint32_t)); ++i)
v[i] = pd->invalid_pte;

- kunmap_local(v);
-
- v = kmap_local_page(pd->p);
+ v = page_address(pd->p);
for (i = 0; i < (PAGE_SIZE / sizeof(uint32_t)); ++i)
v[i] = pd->invalid_pde;

- kunmap_local(v);
-
- clear_page(kmap(pd->dummy_page));
- kunmap(pd->dummy_page);
+ clear_page(page_address(pd->dummy_page));

pd->tables = vmalloc_user(sizeof(struct psb_mmu_pt *) * 1024);
if (!pd->tables)
--
2.25.1

2023-07-24 02:52:54

by Ira Weiny

Subject: Re: [PATCH] Remove unnecessary calls to kmap{,_local_page}() when acquiring pages using GFP_DMA32.

Sumitra Sharma wrote:
> The GFP_DMA32 uses the DMA32 zone to satisfy the allocation
> requests. Therefore, pages allocated with GFP_DMA32 cannot
> come from Highmem.
>
> Avoid using calls to kmap() / kunmap() as the kmap() is being
> deprecated [1].
>
> Avoid using calls to kmap_local_page() / kunmap_local() as the
> code does not depends on the implicit disable of migration of
> local mappings and is, in fact, an unnecessary overhead for
> the main code [2].
>
> Hence, use a plain page_address() directly in the
> psb_mmu_alloc_pd function.
>
> [1]: https://lore.kernel.org/all/[email protected]/
> [2]: https://lwn.net/Articles/836503/
>
> Suggested-by: Ira Weiny <[email protected]>

Reviewed-by: Ira Weiny <[email protected]>

> Signed-off-by: Sumitra Sharma <[email protected]>
> ---
> drivers/gpu/drm/gma500/mmu.c | 11 +++--------
> 1 file changed, 3 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/gma500/mmu.c b/drivers/gpu/drm/gma500/mmu.c
> index a70b01ccdf70..1a44dd062fd1 100644
> --- a/drivers/gpu/drm/gma500/mmu.c
> +++ b/drivers/gpu/drm/gma500/mmu.c
> @@ -184,20 +184,15 @@ struct psb_mmu_pd *psb_mmu_alloc_pd(struct psb_mmu_driver *driver,
> pd->invalid_pte = 0;
> }
>
> - v = kmap_local_page(pd->dummy_pt);
> + v = page_address(pd->dummy_pt);
> for (i = 0; i < (PAGE_SIZE / sizeof(uint32_t)); ++i)
> v[i] = pd->invalid_pte;
>
> - kunmap_local(v);
> -
> - v = kmap_local_page(pd->p);
> + v = page_address(pd->p);
> for (i = 0; i < (PAGE_SIZE / sizeof(uint32_t)); ++i)
> v[i] = pd->invalid_pde;
>
> - kunmap_local(v);
> -
> - clear_page(kmap(pd->dummy_page));
> - kunmap(pd->dummy_page);
> + clear_page(page_address(pd->dummy_page));
>
> pd->tables = vmalloc_user(sizeof(struct psb_mmu_pt *) * 1024);
> if (!pd->tables)
> --
> 2.25.1
>