From: Oleksandr <olekstysh@gmail.com>
To: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Juergen Gross <jgross@suse.com>,
xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Stefano Stabellini <sstabellini@kernel.org>,
Julien Grall <julien@xen.org>,
Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH V2 2/7] xen/grants: support allocating consecutive grants
Date: Mon, 16 May 2022 21:30:21 +0300 [thread overview]
Message-ID: <b2d22549-cdde-1e52-18fd-0ff923b86a5d@gmail.com> (raw)
In-Reply-To: <80286144-cca4-ef07-3aca-2c2374881738@oracle.com>
On 16.05.22 19:00, Boris Ostrovsky wrote:
Hello Boris
>
>
> On 5/16/22 1:59 AM, Juergen Gross wrote:
>> On 14.05.22 04:34, Boris Ostrovsky wrote:
>>>
>>>
>>> On 5/13/22 1:33 AM, Juergen Gross wrote:
>>>> On 12.05.22 22:01, Boris Ostrovsky wrote:
>>>>>
>>>>> On 5/7/22 2:19 PM, Oleksandr Tyshchenko wrote:
>>>
>>>>>> +/* Rebuilds the free grant list and tries to find count
>>>>>> consecutive entries. */
>>>>>> +static int get_free_seq(unsigned int count)
>>>>>> +{
>>>>>> + int ret = -ENOSPC;
>>>>>> + unsigned int from, to;
>>>>>> + grant_ref_t *last;
>>>>>> +
>>>>>> + gnttab_free_tail_ptr = &gnttab_free_head;
>>>>>> + last = &gnttab_free_head;
>>>>>> +
>>>>>> + for (from = find_first_bit(gnttab_free_bitmap, gnttab_size);
>>>>>> + from < gnttab_size;
>>>>>> + from = find_next_bit(gnttab_free_bitmap, gnttab_size,
>>>>>> to + 1)) {
>>>>>> + to = find_next_zero_bit(gnttab_free_bitmap, gnttab_size,
>>>>>> + from + 1);
>>>>>> + if (ret < 0 && to - from >= count) {
>>>>>> + ret = from;
>>>>>> + bitmap_clear(gnttab_free_bitmap, ret, count);
>>>>>> + from += count;
>>>>>> + gnttab_free_count -= count;
>>>>>
>>>>>
>>>>> IIUIC we can have multiple passes over this, meaning that the
>>>>> gnttab_free_count may be decremented more than once. Is that
>>>>> intentional?
>>>>
>>>> After the first pass decrementing gnttab_free_cnt, ret will no
>>>> longer be less than zero, so this can be hit only once.
>>>
>>> Oh, yes, of course.
>>>
>>>>
>>>>>
>>>>>
>>>>>> + if (from == to)
>>>>>> + continue;
>>>>>> + }
>>>>>> +
>>>>>> + while (from < to) {
>>>>>> + *last = from;
>>>>>> + last = __gnttab_entry(from);
>>>>>> + gnttab_last_free = from;
>>>>>> + from++;
>>>>>> + }
>>>>>
>>>>>
>>>>> I have been looking at this loop and I can't understand what it is
>>>>> doing ;-( Can you enlighten me?
>>>>
>>>> It is recreating the free list in order to have it properly sorted.
>>>> This is needed to make sure that the free tail has the maximum
>>>> possible size (you can take the tail off the list without having
>>>> to worry about breaking the linked list because of references into
>>>> the tail).
>>>
>>>
>>> So let's say we have the (one-dimensional) table of length 13
>>>
>>> idx .. 2 3 ... 10 11 12
>>>
>>> grant 12 11 2 -1 3
>>>
>>>
>>> and gnttab_free_head is 10. I.e. the free list is 2, 12, 3, 11.
>>
>> You meant 10, 2, 12, 3, 11, I guess?
>>
>>>
>>> What will this look like after the 2 iterations of the outer loop?
>>
>> idx .. 2 3 ... 10 11 12
>>
>> grant 3 10 11 12 -1
>>
>> with gnttab_free_head being 2, i.e the free list is now 2, 3, 10, 11,
>> 12.
>
>
>
> OK, thanks, that helped. I couldn't link the free chunks in my head
>
>
> With the error handling in gnttab_init() fixed
yes, this is a diff that I am going to apply for the next version:
[snip]
@@ -1596,19 +1601,20 @@ static int gnttab_expand(unsigned int req_entries)
int gnttab_init(void)
{
int i;
- unsigned long max_nr_grant_frames;
+ unsigned long max_nr_grant_frames, max_nr_grefs;
unsigned int max_nr_glist_frames, nr_glist_frames;
int ret;
gnttab_request_version();
max_nr_grant_frames = gnttab_max_grant_frames();
+ max_nr_grefs = max_nr_grant_frames *
+ gnttab_interface->grefs_per_grant_frame;
nr_grant_frames = 1;
/* Determine the maximum number of frames required for the
* grant reference free list on the current hypervisor.
*/
- max_nr_glist_frames = (max_nr_grant_frames *
- gnttab_interface->grefs_per_grant_frame / RPP);
+ max_nr_glist_frames = max_nr_grefs / RPP;
gnttab_list = kmalloc_array(max_nr_glist_frames,
sizeof(grant_ref_t *),
@@ -1625,8 +1631,7 @@ int gnttab_init(void)
}
}
- i = gnttab_interface->grefs_per_grant_frame * max_nr_grant_frames;
- gnttab_free_bitmap = bitmap_zalloc(i, GFP_KERNEL);
+ gnttab_free_bitmap = bitmap_zalloc(max_nr_grefs, GFP_KERNEL);
if (!gnttab_free_bitmap) {
ret = -ENOMEM;
goto ini_nomem;
>
>
> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Thanks!
>
>
>
> -boris
--
Regards,
Oleksandr Tyshchenko
next prev parent reply other threads:[~2022-05-16 18:30 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-07 18:19 [PATCH V2 0/7] virtio: Solution to restrict memory access under Xen using xen-grant DMA-mapping layer Oleksandr Tyshchenko
2022-05-07 18:19 ` [PATCH V2 1/7] arm/xen: Introduce xen_setup_dma_ops() Oleksandr Tyshchenko
2022-05-07 18:52 ` Catalin Marinas
2022-05-07 18:19 ` [PATCH V2 2/7] xen/grants: support allocating consecutive grants Oleksandr Tyshchenko
2022-05-11 18:00 ` Oleksandr
2022-05-11 21:09 ` Boris Ostrovsky
2022-05-12 6:11 ` Oleksandr
2022-05-12 20:01 ` Boris Ostrovsky
2022-05-13 5:33 ` Juergen Gross
2022-05-13 10:43 ` Oleksandr
2022-05-14 2:34 ` Boris Ostrovsky
2022-05-16 5:59 ` Juergen Gross
2022-05-16 16:00 ` Boris Ostrovsky
2022-05-16 18:30 ` Oleksandr [this message]
2022-05-16 18:57 ` Boris Ostrovsky
2022-05-07 18:19 ` [PATCH V2 3/7] xen/grant-dma-ops: Add option to restrict memory access under Xen Oleksandr Tyshchenko
2022-05-09 21:39 ` Stefano Stabellini
2022-05-07 18:19 ` [PATCH V2 4/7] xen/virtio: Enable restricted memory access using Xen grant mappings Oleksandr Tyshchenko
2022-05-09 21:39 ` Stefano Stabellini
2022-05-07 18:19 ` [PATCH V2 5/7] dt-bindings: Add xen,dev-domid property description for xen-grant DMA ops Oleksandr Tyshchenko
2022-05-09 21:39 ` [PATCH V2 5/7] dt-bindings: Add xen, dev-domid " Stefano Stabellini
2022-05-17 0:27 ` [PATCH V2 5/7] dt-bindings: Add xen,dev-domid " Rob Herring
2022-05-18 14:12 ` Oleksandr
2022-05-18 14:32 ` Arnd Bergmann
2022-05-18 16:06 ` Oleksandr
2022-05-18 16:39 ` Arnd Bergmann
2022-05-18 23:32 ` Oleksandr
2022-05-19 1:06 ` Stefano Stabellini
2022-05-19 6:03 ` Oleksandr
2022-05-23 17:30 ` Oleksandr
2022-05-24 1:58 ` Stefano Stabellini
2022-05-24 16:01 ` Rob Herring
2022-05-24 18:34 ` Saravana Kannan
2022-05-25 16:30 ` Oleksandr
2022-05-24 16:11 ` Oleksandr
2022-05-24 17:59 ` Stefano Stabellini
2022-05-25 11:15 ` Oleksandr
2022-05-18 18:59 ` Rob Herring
2022-05-18 23:48 ` Oleksandr
2022-05-07 18:19 ` [PATCH V2 6/7] xen/grant-dma-ops: Retrieve the ID of backend's domain for DT devices Oleksandr Tyshchenko
2022-05-09 21:39 ` Stefano Stabellini
2022-05-07 18:19 ` [PATCH V2 7/7] arm/xen: Assign xen-grant DMA ops for xen-grant DMA devices Oleksandr Tyshchenko
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