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SubjectRe: [PATCH v1 2/2] virtio-mem: prepare fake page onlining code for granularity smaller than MAX_ORDER - 1
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Hi,

On 2021/11/26 21:42, David Hildenbrand wrote:
> Let's prepare our fake page onlining code for subblock size smaller than
> MAX_ORDER - 1: we might get called for ranges not covering properly
> aligned MAX_ORDER - 1 pages. We have to detect the order to use
> dynamically.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> drivers/virtio/virtio_mem.c | 26 +++++++++++++-------------
> 1 file changed, 13 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
> index 03e1c5743699..50de7582c9f8 100644
> --- a/drivers/virtio/virtio_mem.c
> +++ b/drivers/virtio/virtio_mem.c
> @@ -1121,15 +1121,18 @@ static void virtio_mem_clear_fake_offline(unsigned long pfn,
> */
> static void virtio_mem_fake_online(unsigned long pfn, unsigned long nr_pages)
> {
> - const unsigned long max_nr_pages = MAX_ORDER_NR_PAGES;
> + unsigned long order = MAX_ORDER - 1;
> unsigned long i;
>
> /*
> - * We are always called at least with MAX_ORDER_NR_PAGES
> - * granularity/alignment (e.g., the way subblocks work). All pages
> - * inside such a block are alike.
> + * We might get called for ranges that don't cover properly aligned
> + * MAX_ORDER - 1 pages; however, we can only online properly aligned
> + * pages with an order of MAX_ORDER - 1 at maximum.
> */
> - for (i = 0; i < nr_pages; i += max_nr_pages) {
> + while (!IS_ALIGNED(pfn | nr_pages, 1 << order))
> + order--;
> +
> + for (i = 0; i < nr_pages; i += 1 << order) {
> struct page *page = pfn_to_page(pfn + i);
>
> /*
> @@ -1139,14 +1142,12 @@ static void virtio_mem_fake_online(unsigned long pfn, unsigned long nr_pages)
> * alike.
> */
> if (PageDirty(page)) {
> - virtio_mem_clear_fake_offline(pfn + i, max_nr_pages,
> - false);
> - generic_online_page(page, MAX_ORDER - 1);
> + virtio_mem_clear_fake_offline(pfn + i, 1 << order, false);
> + generic_online_page(page, order);
> } else {
> - virtio_mem_clear_fake_offline(pfn + i, max_nr_pages,
> - true);
> - free_contig_range(pfn + i, max_nr_pages);
> - adjust_managed_page_count(page, max_nr_pages);
> + virtio_mem_clear_fake_offline(pfn + i, 1 << order, true);
> + free_contig_range(pfn + i, 1 << order);
> + adjust_managed_page_count(page, 1 << order);
In the loop, pfn + i, 1 << order are repeatedly calculated. 1 << order
is a step size, pfn + i  is each step position.
Better to figure the numer once each iter?

LGTL.
LGTM.
Reviewed-by: Eric Ren <renzhengeek@gmail.com>
> }
> }
> }
> @@ -2477,7 +2478,6 @@ static int virtio_mem_init_hotplug(struct virtio_mem *vm)
> /*
> * We want subblocks to span at least MAX_ORDER_NR_PAGES and
> * pageblock_nr_pages pages. This:
> - * - Simplifies our fake page onlining code (virtio_mem_fake_online).
> * - Is required for now for alloc_contig_range() to work reliably -
> * it doesn't properly handle smaller granularity on ZONE_NORMAL.
> */

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