emm: block: introduce basic flags for ramdisk swap optimization

Upstream: alternative

Currently only for zram and brd, like a stronger version of
QUEUE_FLAG_SYNCHRONOUS, which also indicates that the device requires
runtime page allocation, and may even get accounted.

Signed-off-by: Kairui Song <kasong@tencent.com>

drivers/block/brd.c

@@ -360,6 +360,9 @@ static int brd_alloc(int i)
 	blk_queue_flag_set(QUEUE_FLAG_NONROT, disk->queue);
 	blk_queue_flag_set(QUEUE_FLAG_SYNCHRONOUS, disk->queue);
 	blk_queue_flag_set(QUEUE_FLAG_NOWAIT, disk->queue);
+#ifdef CONFIG_EMM_RAMDISK_SWAP
+	blk_queue_flag_set(QUEUE_FLAG_RAMDISK, disk->queue);
+#endif
 	err = add_disk(disk);
 	if (err)
 		goto out_cleanup_disk;

drivers/block/zram/zram_drv.c

@@ -2220,6 +2220,9 @@ static int zram_add(void)
 	/* zram devices sort of resembles non-rotational disks */
 	blk_queue_flag_set(QUEUE_FLAG_NONROT, zram->disk->queue);
 	blk_queue_flag_set(QUEUE_FLAG_SYNCHRONOUS, zram->disk->queue);
+#ifdef CONFIG_EMM_RAMDISK_SWAP
+	blk_queue_flag_set(QUEUE_FLAG_RAMDISK, zram->disk->queue);
+#endif
 
 	/*
 	 * To ensure that we always get PAGE_SIZE aligned

include/linux/blkdev.h

@@ -573,6 +573,9 @@ struct request_queue {
 #define QUEUE_FLAG_NOWAIT       29	/* device supports NOWAIT */
 #define QUEUE_FLAG_SQ_SCHED     30	/* single queue style io dispatch */
 #define QUEUE_FLAG_SKIP_TAGSET_QUIESCE	31 /* quiesce_tagset skip the queue*/
+#ifdef CONFIG_EMM_RAMDISK_SWAP
+#define QUEUE_FLAG_RAMDISK	32	/* ramdisk requires runtime page alloc */
+#endif
 
 #define QUEUE_FLAG_MQ_DEFAULT	((1UL << QUEUE_FLAG_IO_STAT) |		\
 				 (1UL << QUEUE_FLAG_SAME_COMP) |	\
@@ -1564,4 +1567,15 @@ struct io_comp_batch {
 
 #define DEFINE_IO_COMP_BATCH(name)	struct io_comp_batch name = { }
 
+#ifdef CONFIG_EMM_RAMDISK_SWAP
+/*
+ * Check if a bdev is ramdisk based
+ */
+static inline bool bdev_ramdisk(struct block_device *bdev)
+{
+	return test_bit(QUEUE_FLAG_RAMDISK,
+			&bdev_get_queue(bdev)->queue_flags);
+}
+#endif
+
 #endif /* _LINUX_BLKDEV_H */

mm/Kconfig

@@ -1293,4 +1293,15 @@ config EMM_FORCE_SWAPPINESS
 
 	  If unsure say N.
 
+config EMM_RAMDISK_SWAP
+	bool "Tune ramdisks based swaps"
+	depends on ENHANCED_MM
+	depends on SWAP
+	default n
+	help
+	  This option will enable a few tunes for ramdisk based swaps,
+	  and make swap work better with memcg bounded ramdisk.
+
+	  If unsure say N.
+
 endmenu