Re: [PATCH v2 2/3] dma-buf: system_heap: Add pagepool support to system heap

[Daniel Mentz]

On Fri, Jan 22, 2021 at 7:47 PM John Stultz <john.stultz@xxxxxxxxxx> wrote:
> +static int system_heap_clear_pages(struct page **pages, int num, pgprot_t pgprot)
> +{
> +       void *addr = vmap(pages, num, VM_MAP, pgprot);
> +
> +       if (!addr)
> +               return -ENOMEM;
> +       memset(addr, 0, PAGE_SIZE * num);
> +       vunmap(addr);
> +       return 0;
> +}

I thought that vmap/vunmap are expensive, and I am wondering if
there's a faster way that avoids vmap.

How about lifting this code from lib/iov_iter.c
static void memzero_page(struct page *page, size_t offset, size_t len)
{
        char *addr = kmap_atomic(page);
        memset(addr + offset, 0, len);
        kunmap_atomic(addr);
}

Or what about lifting that code from the old ion_cma_heap.c

if (PageHighMem(pages)) {
        unsigned long nr_clear_pages = nr_pages;
        struct page *page = pages;

        while (nr_clear_pages > 0) {
                void *vaddr = kmap_atomic(page);

                memset(vaddr, 0, PAGE_SIZE);
                kunmap_atomic(vaddr);
                page++;
                nr_clear_pages--;
        }
} else {
        memset(page_address(pages), 0, size);
}