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Subject: Re: [Xen-devel] [RFC 1/3] xen/balloon: Allow allocating DMA buffers
To:     Oleksandr Andrushchenko <andr2000@gmail.com>,
        xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org,
        jgross@suse.com, konrad.wilk@oracle.com
Cc:     daniel.vetter@intel.com, matthew.d.roper@intel.com,
        dongwon.kim@intel.com,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
References: <20180517082604.14828-1-andr2000@gmail.com>
 <20180517082604.14828-2-andr2000@gmail.com>
From:   Boris Ostrovsky <boris.ostrovsky@oracle.com>
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Message-ID: <6a108876-19b7-49d0-3de2-9e10f984736c@oracle.com>
Date:   Fri, 18 May 2018 18:04:07 -0400
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Sender: linux-kernel-owner@vger.kernel.org
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On 05/17/2018 04:26 AM, Oleksandr Andrushchenko wrote:
> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>


A commit message would be useful.


>
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>
>  	for (i = 0; i < nr_pages; i++) {
> -		page = alloc_page(gfp);
> -		if (page == NULL) {
> -			nr_pages = i;
> -			state = BP_EAGAIN;
> -			break;
> +		if (ext_pages) {
> +			page = ext_pages[i];
> +		} else {
> +			page = alloc_page(gfp);
> +			if (page == NULL) {
> +				nr_pages = i;
> +				state = BP_EAGAIN;
> +				break;
> +			}
>  		}
>  		scrub_page(page);
>  		list_add(&page->lru, &pages);
> @@ -529,7 +565,7 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
>  	i = 0;
>  	list_for_each_entry_safe(page, tmp, &pages, lru) {
>  		/* XENMEM_decrease_reservation requires a GFN */
> -		frame_list[i++] = xen_page_to_gfn(page);
> +		frames[i++] = xen_page_to_gfn(page);
>  
>  #ifdef CONFIG_XEN_HAVE_PVMMU
>  		/*
> @@ -552,18 +588,22 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
>  #endif
>  		list_del(&page->lru);
>  
> -		balloon_append(page);
> +		if (!ext_pages)
> +			balloon_append(page);


So what you are proposing is not really ballooning. You are just
piggybacking on existing interfaces, aren't you?

-boris