Re: [PATCH kernel 1/2] powerpc/iommu: Allocate it_map by vmalloc

[Leonardo Bras <leobras.c@gmail.com>]

On Tue, 2021-02-16 at 14:33 +1100, Alexey Kardashevskiy wrote:
> The IOMMU table uses the it_map bitmap to keep track of allocated DMA
> pages. This has always been a contiguous array allocated at either
> the boot time or when a passed through device is returned to the host OS.
> The it_map memory is allocated by alloc_pages() which allocates
> contiguous physical memory.
> 
> Such allocation method occasionally creates a problem when there is
> no big chunk of memory available (no free memory or too fragmented).
> On powernv/ioda2 the default DMA window requires 16MB for it_map.
> 
> This replaces alloc_pages_node() with vzalloc_node() which allocates
> contiguous block but in virtual memory. This should reduce changes of
> failure but should not cause other behavioral changes as it_map is only
> used by the kernel's DMA hooks/api when MMU is on.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

It looks a very good change, and also makes code much simpler to read.

FWIW:

Reviewed-by: Leonardo Bras <leobras.c@gmail,com>

> ---
>  arch/powerpc/kernel/iommu.c | 15 +++------------
>  1 file changed, 3 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
> index c00214a4355c..8eb6eb0afa97 100644
> --- a/arch/powerpc/kernel/iommu.c
> +++ b/arch/powerpc/kernel/iommu.c
> @@ -719,7 +719,6 @@ struct iommu_table *iommu_init_table(struct iommu_table *tbl, int nid,
>  {
>  	unsigned long sz;
>  	static int welcomed = 0;
> -	struct page *page;
>  	unsigned int i;
>  	struct iommu_pool *p;
>  
> 
> 
> 
> @@ -728,11 +727,9 @@ struct iommu_table *iommu_init_table(struct iommu_table *tbl, int nid,
>  	/* number of bytes needed for the bitmap */
>  	sz = BITS_TO_LONGS(tbl->it_size) * sizeof(unsigned long);
>  
> 
> 
> 
> -	page = alloc_pages_node(nid, GFP_KERNEL, get_order(sz));
> -	if (!page)
> +	tbl->it_map = vzalloc_node(sz, nid);
> +	if (!tbl->it_map)
>  		panic("iommu_init_table: Can't allocate %ld bytes\n", sz);
> -	tbl->it_map = page_address(page);
> -	memset(tbl->it_map, 0, sz);
>  
> 
> 
> 
>  	iommu_table_reserve_pages(tbl, res_start, res_end);
>  
> 
> 
> 
> @@ -774,8 +771,6 @@ struct iommu_table *iommu_init_table(struct iommu_table *tbl, int nid,
>  
> 
> 
> 
>  static void iommu_table_free(struct kref *kref)
>  {
> -	unsigned long bitmap_sz;
> -	unsigned int order;
>  	struct iommu_table *tbl;
>  
> 
> 
> 
>  	tbl = container_of(kref, struct iommu_table, it_kref);
> @@ -796,12 +791,8 @@ static void iommu_table_free(struct kref *kref)
>  	if (!bitmap_empty(tbl->it_map, tbl->it_size))
>  		pr_warn("%s: Unexpected TCEs\n", __func__);
>  
> 
> 
> 
> -	/* calculate bitmap size in bytes */
> -	bitmap_sz = BITS_TO_LONGS(tbl->it_size) * sizeof(unsigned long);
> -
>  	/* free bitmap */
> -	order = get_order(bitmap_sz);
> -	free_pages((unsigned long) tbl->it_map, order);
> +	vfree(tbl->it_map);
>  
> 
> 
> 
>  	/* free table */
>  	kfree(tbl);