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Subject[PATCH v2 3/4] mm:swap: introduce SWP_SYNCHRONOUS_IO
Date
If rw-page based fast storage is used for swap devices, we need to
detect it to enhance swap IO operations.
This patch is preparation for optimizing of swap-in operation with
next patch.

Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
include/linux/swap.h | 3 ++-
mm/swapfile.c | 3 +++
2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 8a807292037f..fbb33919d1c6 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -170,8 +170,9 @@ enum {
SWP_AREA_DISCARD = (1 << 8), /* single-time swap area discards */
SWP_PAGE_DISCARD = (1 << 9), /* freed swap page-cluster discards */
SWP_STABLE_WRITES = (1 << 10), /* no overwrite PG_writeback pages */
+ SWP_SYNCHRONOUS_IO = (1 << 11), /* synchronous IO is efficient */
/* add others here before... */
- SWP_SCANNING = (1 << 11), /* refcount in scan_swap_map */
+ SWP_SCANNING = (1 << 12), /* refcount in scan_swap_map */
};

#define SWAP_CLUSTER_MAX 32UL
diff --git a/mm/swapfile.c b/mm/swapfile.c
index bf91dc9e7a79..1305591cde4d 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3168,6 +3168,9 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
if (bdi_cap_stable_pages_required(inode_to_bdi(inode)))
p->flags |= SWP_STABLE_WRITES;

+ if (bdi_cap_synchronous_io(inode_to_bdi(inode)))
+ p->flags |= SWP_SYNCHRONOUS_IO;
+
if (p->bdev && blk_queue_nonrot(bdev_get_queue(p->bdev))) {
int cpu;
unsigned long ci, nr_cluster;
--
2.7.4
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