linux-kernel - Re: [Xen-devel] [RFC 1/3] xen/balloon: Allow allocating DMA buffers

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Date:   Mon, 21 May 2018 08:40:30 +0300
From:   Oleksandr Andrushchenko <andr2000@...il.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-media@...r.kernel.org,
        jgross@...e.com, konrad.wilk@...cle.com
Cc:     daniel.vetter@...el.com, matthew.d.roper@...el.com,
        dongwon.kim@...el.com,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
Subject: Re: [Xen-devel] [RFC 1/3] xen/balloon: Allow allocating DMA buffers

On 05/19/2018 01:04 AM, Boris Ostrovsky wrote:
> On 05/17/2018 04:26 AM, Oleksandr Andrushchenko wrote:
>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
>
> A commit message would be useful.
Sure, v1 will have it
>
>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.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?
Sort of. Basically I need to {increase|decrease}_reservation, not actually
allocating ballooned pages.
Do you think I can simply EXPORT_SYMBOL for {increase|decrease}_reservation?
Any other suggestion?
> -boris
>
>
Thank you,
Oleksandr