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Date: Fri, 16 Oct 2020 15:15:02 +0800
From: Wei Yang <richard.weiyang@...ux.alibaba.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
virtualization@...ts.linux-foundation.org,
Andrew Morton <akpm@...ux-foundation.org>,
"Michael S . Tsirkin" <mst@...hat.com>,
Jason Wang <jasowang@...hat.com>,
Pankaj Gupta <pankaj.gupta.linux@...il.com>
Subject: Re: [PATCH v1 13/29] virtio-mem: factor out handling of fake-offline
pages in memory notifier
On Mon, Oct 12, 2020 at 02:53:07PM +0200, David Hildenbrand wrote:
>Let's factor out the core pieces and place the implementation next to
>virtio_mem_fake_offline(). We'll reuse this functionality soon.
>
>Cc: "Michael S. Tsirkin" <mst@...hat.com>
>Cc: Jason Wang <jasowang@...hat.com>
>Cc: Pankaj Gupta <pankaj.gupta.linux@...il.com>
>Signed-off-by: David Hildenbrand <david@...hat.com>
>---
> drivers/virtio/virtio_mem.c | 73 +++++++++++++++++++++++++------------
> 1 file changed, 50 insertions(+), 23 deletions(-)
>
>diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
>index d132bc54ef57..a2124892e510 100644
>--- a/drivers/virtio/virtio_mem.c
>+++ b/drivers/virtio/virtio_mem.c
>@@ -168,6 +168,10 @@ static LIST_HEAD(virtio_mem_devices);
>
> static void virtio_mem_online_page_cb(struct page *page, unsigned int order);
> static void virtio_mem_retry(struct virtio_mem *vm);
>+static void virtio_mem_fake_offline_going_offline(unsigned long pfn,
>+ unsigned long nr_pages);
>+static void virtio_mem_fake_offline_cancel_offline(unsigned long pfn,
>+ unsigned long nr_pages);
>
> /*
> * Register a virtio-mem device so it will be considered for the online_page
>@@ -604,27 +608,15 @@ static void virtio_mem_notify_going_offline(struct virtio_mem *vm,
> unsigned long mb_id)
> {
> const unsigned long nr_pages = PFN_DOWN(vm->subblock_size);
>- struct page *page;
> unsigned long pfn;
>- int sb_id, i;
>+ int sb_id;
>
> for (sb_id = 0; sb_id < vm->nb_sb_per_mb; sb_id++) {
> if (virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id, 1))
> continue;
>- /*
>- * Drop our reference to the pages so the memory can get
>- * offlined and add the unplugged pages to the managed
>- * page counters (so offlining code can correctly subtract
>- * them again).
>- */
> pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
> sb_id * vm->subblock_size);
>- adjust_managed_page_count(pfn_to_page(pfn), nr_pages);
One question about the original code, why we want to adjust count here?
The code flow is
__offline_pages()
memory_notify(MEM_GOING_OFFLINE, &arg)
virtio_mem_notify_going_offline(vm, mb_id)
adjust_managed_page_count(pfn_to_page(pfn), nr_pages)
adjust_managed_page_count(pfn_to_page(start_pfn), -offlined_pages)
Do we adjust the count twice?
>- for (i = 0; i < nr_pages; i++) {
>- page = pfn_to_page(pfn + i);
>- if (WARN_ON(!page_ref_dec_and_test(page)))
>- dump_page(page, "unplugged page referenced");
>- }
>+ virtio_mem_fake_offline_going_offline(pfn, nr_pages);
> }
> }
>
>@@ -633,21 +625,14 @@ static void virtio_mem_notify_cancel_offline(struct virtio_mem *vm,
> {
> const unsigned long nr_pages = PFN_DOWN(vm->subblock_size);
> unsigned long pfn;
>- int sb_id, i;
>+ int sb_id;
>
> for (sb_id = 0; sb_id < vm->nb_sb_per_mb; sb_id++) {
> if (virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id, 1))
> continue;
>- /*
>- * Get the reference we dropped when going offline and
>- * subtract the unplugged pages from the managed page
>- * counters.
>- */
> pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
> sb_id * vm->subblock_size);
>- adjust_managed_page_count(pfn_to_page(pfn), -nr_pages);
>- for (i = 0; i < nr_pages; i++)
>- page_ref_inc(pfn_to_page(pfn + i));
>+ virtio_mem_fake_offline_cancel_offline(pfn, nr_pages);
> }
> }
>
>@@ -853,6 +838,48 @@ static int virtio_mem_fake_offline(unsigned long pfn, unsigned long nr_pages)
> return 0;
> }
>
>+/*
>+ * Handle fake-offline pages when memory is going offline - such that the
>+ * pages can be skipped by mm-core when offlining.
>+ */
>+static void virtio_mem_fake_offline_going_offline(unsigned long pfn,
>+ unsigned long nr_pages)
>+{
>+ struct page *page;
>+ unsigned long i;
>+
>+ /*
>+ * Drop our reference to the pages so the memory can get offlined
>+ * and add the unplugged pages to the managed page counters (so
>+ * offlining code can correctly subtract them again).
>+ */
>+ adjust_managed_page_count(pfn_to_page(pfn), nr_pages);
>+ /* Drop our reference to the pages so the memory can get offlined. */
>+ for (i = 0; i < nr_pages; i++) {
>+ page = pfn_to_page(pfn + i);
>+ if (WARN_ON(!page_ref_dec_and_test(page)))
>+ dump_page(page, "fake-offline page referenced");
>+ }
>+}
>+
>+/*
>+ * Handle fake-offline pages when memory offlining is canceled - to undo
>+ * what we did in virtio_mem_fake_offline_going_offline().
>+ */
>+static void virtio_mem_fake_offline_cancel_offline(unsigned long pfn,
>+ unsigned long nr_pages)
>+{
>+ unsigned long i;
>+
>+ /*
>+ * Get the reference we dropped when going offline and subtract the
>+ * unplugged pages from the managed page counters.
>+ */
>+ adjust_managed_page_count(pfn_to_page(pfn), -nr_pages);
>+ for (i = 0; i < nr_pages; i++)
>+ page_ref_inc(pfn_to_page(pfn + i));
>+}
>+
> static void virtio_mem_online_page_cb(struct page *page, unsigned int order)
> {
> const unsigned long addr = page_to_phys(page);
>--
>2.26.2
--
Wei Yang
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