zram: implement rw_page operation of zram

This patch implements rw_page operation for zram block device.

I implemented the feature in zram and tested it.  Test bed was the G2, LG
electronic mobile device, whtich has msm8974 processor and 2GB memory.

With a memory allocation test program consuming memory, the system
generates swap.

Operating time of swap_write_page() was measured.

--------------------------------------------------
|             |   operating time   | improvement |
|             |  (20 runs average) |             |
--------------------------------------------------
|with patch   |    1061.15 us      |    +2.4%    |
--------------------------------------------------
|without patch|    1087.35 us      |             |
--------------------------------------------------

Each test(with paged_io,with BIO) result set shows normal distribution and
has equal variance.  I mean the two values are valid result to compare.  I
can say operation with paged I/O(without BIO) is faster 2.4% with
confidence level 95%.

[minchan@kernel.org: make rw_page opeartion return 0]
[minchan@kernel.org: rely on the bi_end_io for zram_rw_page fails]
[sergey.senozhatsky@gmail.com: code cleanup]
[minchan@kernel.org: add comment]
Signed-off-by: karam.lee <karam.lee@lge.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
Cc: Matthew Wilcox <matthew.r.wilcox@intel.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: <seungho1.park@lge.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 44 insertions, 0 deletions

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 98af4aae2618..976eab6f35b9 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -945,8 +945,52 @@ static void zram_slot_free_notify(struct block_device *bdev,
         atomic64_inc(&zram->stats.notify_free);
 }
 
+static int zram_rw_page(struct block_device *bdev, sector_t sector,
+                       struct page *page, int rw)
+{
+        int offset, err;
+        u32 index;
+        struct zram *zram;
+        struct bio_vec bv;
+
+        zram = bdev->bd_disk->private_data;
+        if (!valid_io_request(zram, sector, PAGE_SIZE)) {
+                atomic64_inc(&zram->stats.invalid_io);
+                return -EINVAL;
+        }
+
+        down_read(&zram->init_lock);
+        if (unlikely(!init_done(zram))) {
+                err = -EIO;
+                goto out_unlock;
+        }
+
+        index = sector >> SECTORS_PER_PAGE_SHIFT;
+        offset = sector & (SECTORS_PER_PAGE - 1) << SECTOR_SHIFT;
+
+        bv.bv_page = page;
+        bv.bv_len = PAGE_SIZE;
+        bv.bv_offset = 0;
+
+        err = zram_bvec_rw(zram, &bv, index, offset, rw);
+out_unlock:
+        up_read(&zram->init_lock);
+        /*
+         * If I/O fails, just return error(ie, non-zero) without
+         * calling page_endio.
+         * It causes resubmit the I/O with bio request by upper functions
+         * of rw_page(e.g., swap_readpage, __swap_writepage) and
+         * bio->bi_end_io does things to handle the error
+         * (e.g., SetPageError, set_page_dirty and extra works).
+         */
+        if (err == 0)
+                page_endio(page, rw, 0);
+        return err;
+}
+
 static const struct block_device_operations zram_devops = {
         .swap_slot_free_notify = zram_slot_free_notify,
+        .rw_page = zram_rw_page,
         .owner = THIS_MODULE
 };