Currently zram will adjust its fops to a version which does not
contain rw_page when a backing device has been assigned. This is
done to prevent upper layers from assuming a synchronous operation
when a page may have been written back. This forces every operation
through bio which has overhead associated with bio_alloc/frees.
The code can be simplified to always expose a rw_page method and
only in the rare event that a page is written back we instead will
return -EOPNOTSUPP forcing the upper layer to fallback to bio.
Signed-off-by: Brian Geffon <bgeffon@xxxxxxxxxx>
---
drivers/block/zram/zram_drv.c | 26 +++-----------------------
1 file changed, 3 insertions(+), 23 deletions(-)
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 226ea76cc819..b9646886be0f 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -52,9 +52,6 @@ static unsigned int num_devices = 1;
static size_t huge_class_size;
static const struct block_device_operations zram_devops;
-#ifdef CONFIG_ZRAM_WRITEBACK
-static const struct block_device_operations zram_wb_devops;
-#endif
static void zram_free_page(struct zram *zram, size_t index);
static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
@@ -543,17 +540,6 @@ static ssize_t backing_dev_store(struct device *dev,
zram->backing_dev = backing_dev;
zram->bitmap = bitmap;
zram->nr_pages = nr_pages;
- /*
- * With writeback feature, zram does asynchronous IO so it's no longer
- * synchronous device so let's remove synchronous io flag. Othewise,
- * upper layer(e.g., swap) could wait IO completion rather than
- * (submit and return), which will cause system sluggish.
- * Furthermore, when the IO function returns(e.g., swap_readpage),
- * upper layer expects IO was done so it could deallocate the page
- * freely but in fact, IO is going on so finally could cause
- * use-after-free when the IO is really done.
- */
- zram->disk->fops = &zram_wb_devops;
up_write(&zram->init_lock);
pr_info("setup backing device %s\n", file_name);
@@ -1267,6 +1253,9 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
struct bio_vec bvec;
zram_slot_unlock(zram, index);
+ /* If we don't have a bio we came via rw_page, we must fallback to bio */
+ if (!bio)
+ return -EOPNOTSUPP;
bvec.bv_page = page;
bvec.bv_len = PAGE_SIZE;
@@ -1848,15 +1837,6 @@ static const struct block_device_operations zram_devops = {
.owner = THIS_MODULE
};
-#ifdef CONFIG_ZRAM_WRITEBACK
-static const struct block_device_operations zram_wb_devops = {
- .open = zram_open,
- .submit_bio = zram_submit_bio,
- .swap_slot_free_notify = zram_slot_free_notify,
- .owner = THIS_MODULE
-};
-#endif
-
static DEVICE_ATTR_WO(compact);
static DEVICE_ATTR_RW(disksize);
static DEVICE_ATTR_RO(initstate);
--
2.38.0.rc1.362.ged0d419d3c-goog
