[PATCH v1 14/29] virtio-mem: retry fake-offlining via alloc_contig_range() on ZONE_MOVABLE
From: David Hildenbrand <hidden>
Date: 2020-10-12 12:55:26
Also in:
linux-mm, lkml
Subsystem:
the rest, virtio core, virtio mem driver · Maintainers:
Linus Torvalds, "Michael S. Tsirkin", Jason Wang, David Hildenbrand
ZONE_MOVABLE is supposed to give some guarantees, yet, alloc_contig_range() isn't prepared to properly deal with some racy cases properly (e.g., temporary page pinning when exiting processed, PCP). Retry 5 times for now. There is certainly room for improvement in the future. Cc: "Michael S. Tsirkin" <mst@redhat.com> Cc: Jason Wang <jasowang@redhat.com> Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com> Signed-off-by: David Hildenbrand <redacted> --- drivers/virtio/virtio_mem.c | 37 ++++++++++++++++++++++++++----------- 1 file changed, 26 insertions(+), 11 deletions(-)
diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index a2124892e510..faeb759687fe 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c@@ -823,19 +823,34 @@ static void virtio_mem_fake_online(unsigned long pfn, unsigned long nr_pages) */ static int virtio_mem_fake_offline(unsigned long pfn, unsigned long nr_pages) { - int rc; + const bool is_movable = zone_idx(page_zone(pfn_to_page(pfn))) == + ZONE_MOVABLE; + int rc, retry_count; - rc = alloc_contig_range(pfn, pfn + nr_pages, MIGRATE_MOVABLE, - GFP_KERNEL); - if (rc == -ENOMEM) - /* whoops, out of memory */ - return rc; - if (rc) - return -EBUSY; + /* + * TODO: We want an alloc_contig_range() mode that tries to allocate + * harder (e.g., dealing with temporarily pinned pages, PCP), especially + * with ZONE_MOVABLE. So for now, retry a couple of times with + * ZONE_MOVABLE before giving up - because that zone is supposed to give + * some guarantees. + */ + for (retry_count = 0; retry_count < 5; retry_count++) { + rc = alloc_contig_range(pfn, pfn + nr_pages, MIGRATE_MOVABLE, + GFP_KERNEL); + if (rc == -ENOMEM) + /* whoops, out of memory */ + return rc; + else if (rc && !is_movable) + break; + else if (rc) + continue; - virtio_mem_set_fake_offline(pfn, nr_pages, true); - adjust_managed_page_count(pfn_to_page(pfn), -nr_pages); - return 0; + virtio_mem_set_fake_offline(pfn, nr_pages, true); + adjust_managed_page_count(pfn_to_page(pfn), -nr_pages); + return 0; + } + + return -EBUSY; } /*
--
2.26.2
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