Messages in this thread Patch in this message | | | Date | Fri, 15 Nov 2019 14:55:57 -0800 | Subject | [PATCH] virtio_balloon: fix shrinker pages_to_free calculation | From | Khazhismel Kumykov <> |
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To my reading, we're accumulating total freed pages in pages_freed, but subtracting it every iteration from pages_to_free, meaning we'll count earlier iterations multiple times, freeing fewer pages than expected. Just accumulate in pages_freed, and compare to pages_to_free.
There's also a unit mismatch, where pages_to_free seems to be virtio balloon pages, and pages_freed is system pages (We divide by VIRTIO_BALLOON_PAGES_PER_PAGE), so sutracting pages_freed from pages_to_free may result in freeing too much.
There also seems to be a mismatch between shrink_free_pages() and shrink_balloon_pages(), where in both pages_to_free is given as # of virtio pages to free, but free_pages() returns virtio pages, and balloon_pages returns system pages.
(For 4K PAGE_SIZE, this mismatch wouldn't be noticed since VIRTIO_BALLOON_PAGES_PER_PAGE would be 1)
Have both return virtio pages, and divide into system pages when returning from shrinker_scan()
Fixes: 71994620bb25 ("virtio_balloon: replace oom notifier with shrinker") Cc: Wei Wang <wei.w.wang@intel.com> Signed-off-by: Khazhismel Kumykov <khazhy@google.com> ---
Tested this under memory pressure conditions and the shrinker seemed to shrink.
drivers/virtio/virtio_balloon.c | 11 ++++------- 1 file changed, 4 insertions(+), 7 deletions(-)
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c index 226fbb995fb0..7951ece3fe24 100644 --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -782,11 +782,8 @@ static unsigned long shrink_balloon_pages(struct virtio_balloon *vb, * VIRTIO_BALLOON_ARRAY_PFNS_MAX balloon pages, so we call it * multiple times to deflate pages till reaching pages_to_free. */ - while (vb->num_pages && pages_to_free) { - pages_freed += leak_balloon(vb, pages_to_free) / - VIRTIO_BALLOON_PAGES_PER_PAGE; - pages_to_free -= pages_freed; - } + while (vb->num_pages && pages_to_free > pages_freed) + pages_freed += leak_balloon(vb, pages_to_free - pages_freed); update_balloon_size(vb); return pages_freed; @@ -805,11 +802,11 @@ static unsigned long virtio_balloon_shrinker_scan(struct shrinker *shrinker, pages_freed = shrink_free_pages(vb, pages_to_free); if (pages_freed >= pages_to_free) - return pages_freed; + return pages_freed / VIRTIO_BALLOON_PAGES_PER_PAGE; pages_freed += shrink_balloon_pages(vb, pages_to_free - pages_freed); - return pages_freed; + return pages_freed / VIRTIO_BALLOON_PAGES_PER_PAGE; } static unsigned long virtio_balloon_shrinker_count(struct shrinker *shrinker, -- 2.24.0.432.g9d3f5f5b63-goog
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