From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751249AbeEUSuM (ORCPT ); Mon, 21 May 2018 14:50:12 -0400 Received: from userp2130.oracle.com ([156.151.31.86]:40156 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750923AbeEUSuI (ORCPT ); Mon, 21 May 2018 14:50:08 -0400 Subject: Re: [Xen-devel] [RFC 1/3] xen/balloon: Allow allocating DMA buffers To: Oleksandr Andrushchenko , 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 References: <20180517082604.14828-1-andr2000@gmail.com> <20180517082604.14828-2-andr2000@gmail.com> <6a108876-19b7-49d0-3de2-9e10f984736c@oracle.com> <9541926e-001a-e41e-317c-dbff6d687761@gmail.com> <218e2bf7-490d-f89e-9866-27b7e3dbc835@oracle.com> From: Boris Ostrovsky Openpgp: preference=signencrypt Autocrypt: addr=boris.ostrovsky@oracle.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8900 signatures=668700 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1711220000 definitions=main-1805210222 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/21/2018 01:32 PM, Oleksandr Andrushchenko wrote: > On 05/21/2018 07:35 PM, Boris Ostrovsky wrote: >> On 05/21/2018 01:40 AM, Oleksandr Andrushchenko wrote: >>> On 05/19/2018 01:04 AM, Boris Ostrovsky wrote: >>>> On 05/17/2018 04:26 AM, Oleksandr Andrushchenko wrote: >>>>> From: Oleksandr Andrushchenko >>>> A commit message would be useful. >>> Sure, v1 will have it >>>>> Signed-off-by: Oleksandr Andrushchenko >>>>> >>>>> >>>>>        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? >> >> I am actually wondering how much of that code you end up reusing. You >> pretty much create new code paths in both routines and common code ends >> up being essentially the hypercall. > Well, I hoped that it would be easier to maintain if I modify existing > code > to support both use-cases, but I am also ok to create new routines if > this > seems to be reasonable - please let me know >>   So the question is --- would it make >> sense to do all of this separately from the balloon driver? > This can be done, but which driver will host this code then? If we > move from > the balloon driver, then this could go to either gntdev or grant-table. > What's your preference? A separate module? Is there any use for this feature outside of your zero-copy DRM driver? -boris