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

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Message-ID: <CAE2F3rA3a-MWBHPZhGP9dMhEUqMkkvm6wXYYh6LDZ1zF9CAyUg@mail.gmail.com>
Date:   Wed, 27 Jan 2021 12:21:15 -0800
From:   Daniel Mentz <danielmentz@...gle.com>
To:     John Stultz <john.stultz@...aro.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Liam Mark <lmark@...eaurora.org>,
        Chris Goldsworthy <cgoldswo@...eaurora.org>,
        Laura Abbott <labbott@...nel.org>,
        Brian Starkey <Brian.Starkey@....com>,
        Hridya Valsaraju <hridya@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Sandeep Patil <sspatil@...gle.com>,
        Ørjan Eide <orjan.eide@....com>,
        Robin Murphy <robin.murphy@....com>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Simon Ser <contact@...rsion.fr>,
        James Jones <jajones@...dia.com>, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2 2/3] dma-buf: system_heap: Add pagepool support to
 system heap

On Fri, Jan 22, 2021 at 7:47 PM John Stultz <john.stultz@...aro.org> 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);
}