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Subject: Re: [PATCH 2/8] xen/balloon: Move common memory reservation routines
 to a module
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, dongwon.kim@intel.com,
        matthew.d.roper@intel.com,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
References: <20180525153331.31188-1-andr2000@gmail.com>
 <20180525153331.31188-3-andr2000@gmail.com>
 <59ab73b0-967b-a82f-3b0d-95f1b0dc40a5@oracle.com>
 <89de7bdb-8759-419f-63bf-8ed0d57650f0@gmail.com>
From:   Boris Ostrovsky <boris.ostrovsky@oracle.com>
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Message-ID: <edfa937b-3311-98db-2e6f-b4083598f796@oracle.com>
Date:   Tue, 29 May 2018 16:03:09 -0400
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Sender: linux-kernel-owner@vger.kernel.org
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On 05/29/2018 02:22 PM, Oleksandr Andrushchenko wrote:
> On 05/29/2018 09:04 PM, Boris Ostrovsky wrote:
>> On 05/25/2018 11:33 AM, Oleksandr Andrushchenko wrote:

>> @@ -463,11 +457,6 @@ static enum bp_state
>> increase_reservation(unsigned long nr_pages)
>>       int rc;
>>       unsigned long i;
>>       struct page   *page;
>> -    struct xen_memory_reservation reservation = {
>> -        .address_bits = 0,
>> -        .extent_order = EXTENT_ORDER,
>> -        .domid        = DOMID_SELF
>> -    };
>>         if (nr_pages > ARRAY_SIZE(frame_list))
>>           nr_pages = ARRAY_SIZE(frame_list);
>> @@ -486,9 +475,7 @@ static enum bp_state
>> increase_reservation(unsigned long nr_pages)
>>           page = balloon_next_page(page);
>>       }
>>   -    set_xen_guest_handle(reservation.extent_start, frame_list);
>> -    reservation.nr_extents = nr_pages;
>> -    rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
>> +    rc = xenmem_reservation_increase(nr_pages, frame_list);
>>       if (rc <= 0)
>>           return BP_EAGAIN;
>>   @@ -496,29 +483,7 @@ static enum bp_state
>> increase_reservation(unsigned long nr_pages)
>>           page = balloon_retrieve(false);
>>           BUG_ON(page == NULL);
>>   -#ifdef CONFIG_XEN_HAVE_PVMMU
>> -        /*
>> -         * We don't support PV MMU when Linux and Xen is using
>> -         * different page granularity.
>> -         */
>> -        BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
>> -
>> -        if (!xen_feature(XENFEAT_auto_translated_physmap)) {
>> -            unsigned long pfn = page_to_pfn(page);
>> -
>> -            set_phys_to_machine(pfn, frame_list[i]);
>> -
>> -            /* Link back into the page tables if not highmem. */
>> -            if (!PageHighMem(page)) {
>> -                int ret;
>> -                ret = HYPERVISOR_update_va_mapping(
>> -                        (unsigned long)__va(pfn << PAGE_SHIFT),
>> -                        mfn_pte(frame_list[i], PAGE_KERNEL),
>> -                        0);
>> -                BUG_ON(ret);
>> -            }
>> -        }
>> -#endif
>> +        xenmem_reservation_va_mapping_update(1, &page, &frame_list[i]);
>>
>> Can you make a single call to xenmem_reservation_va_mapping_update(rc,
>> ...)? You need to keep track of pages but presumable they can be put
>> into an array (or a list). In fact, perhaps we can have
>> balloon_retrieve() return a set of pages.
> This is actually how it is used later on for dma-buf, but I just
> didn't want
> to alter original balloon code too much, but this can be done, in
> order of simplicity:
>
> 1. Similar to frame_list, e.g. static array of struct page* of size
> ARRAY_SIZE(frame_list):
> more static memory is used, but no allocations
>
> 2. Allocated at run-time with kcalloc: allocation can fail


If this is called in freeing DMA buffer code path or in error path then
we shouldn't do it.


>
> 3. Make balloon_retrieve() return a set of pages: will require
> list/array allocation
> and handling, allocation may fail, balloon_retrieve prototype change


balloon pages are strung on the lru list. Can we keep have
balloon_retrieve return a list of pages on that list?

-boris


>
> Could you please tell which of the above will fit better?
>
>>
>>