This patch implement SWAP_GET_FREE handler in zram so that VM can
know how many zram has freeable space.
VM can use it to stop anonymous reclaiming once zram is full.

Signed-off-by: Minchan Kim <minc...@kernel.org>
---
 drivers/block/zram/zram_drv.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 88661d62e46a..8e22b20aa2db 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -951,6 +951,22 @@ static int zram_slot_free_notify(struct block_device *bdev,
        return 0;
 }
 
+static int zram_get_free_pages(struct block_device *bdev, long *free)
+{
+       struct zram *zram;
+       struct zram_meta *meta;
+
+       zram = bdev->bd_disk->private_data;
+       meta = zram->meta;
+
+       if (!zram->limit_pages)
+               return 1;
+
+       *free = zram->limit_pages - zs_get_total_pages(meta->mem_pool);
+
+       return 0;
+}
+
 static int zram_swap_hint(struct block_device *bdev,
                                unsigned int hint, void *arg)
 {
@@ -958,6 +974,8 @@ static int zram_swap_hint(struct block_device *bdev,
 
        if (hint == SWAP_SLOT_FREE)
                ret = zram_slot_free_notify(bdev, (unsigned long)arg);
+       else if (hint == SWAP_GET_FREE)
+               ret = zram_get_free_pages(bdev, arg);
 
        return ret;
 }
-- 
2.0.0

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