From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753317AbeEURcY (ORCPT ); Mon, 21 May 2018 13:32:24 -0400 Received: from mail-lf0-f67.google.com ([209.85.215.67]:39850 "EHLO mail-lf0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753097AbeEURcU (ORCPT ); Mon, 21 May 2018 13:32:20 -0400 X-Google-Smtp-Source: AB8JxZo342VVCYleyJeNhwaWHgjpOV1VY5mlTX9wgMvjQRqFotA2FmZxt5FCIK3pd7Dam3RWI751Cw== Subject: Re: [Xen-devel] [RFC 1/3] xen/balloon: Allow allocating DMA buffers To: Boris Ostrovsky , 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: Oleksandr Andrushchenko Message-ID: Date: Mon, 21 May 2018 20:32:15 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <218e2bf7-490d-f89e-9866-27b7e3dbc835@oracle.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? > > -boris Thank you, Oleksandr