linux-kernel - Re: [PATCH] Remove unnecessary calls to kmap{,_local_page}() when acquiring pages using GFP

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Date:   Sun, 23 Jul 2023 19:25:06 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Sumitra Sharma <sumitraartsy@...il.com>,
        Patrik Jakobsson <patrik.r.jakobsson@...il.com>,
        David Airlie <airlied@...il.com>,
        "Daniel Vetter" <daniel@...ll.ch>,
        <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Fabio <fmdefrancesco@...il.com>, Deepak R Varma <drv@...lo.com>,
        Alison Schofield <alison.schofield@...el.com>
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/20220813220034.806698-1-ira.weiny@intel.com/
> [2]: https://lwn.net/Articles/836503/
> 
> Suggested-by: Ira Weiny <ira.weiny@...el.com>

Reviewed-by: Ira Weiny <ira.weiny@...el.com>

> Signed-off-by: Sumitra Sharma <sumitraartsy@...il.com>
> ---
>  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
>