mm, swap: introduce SWP_SYNCHRONOUS_IO

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.

Link: http://lkml.kernel.org/r/1505886205-9671-4-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Ilya Dryomov <idryomov@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Huang Ying <ying.huang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/swap.h b/include/linux/swap.h
index f02fb5db8914bf0731c03ae80e444156ec83a3cb..933d7c0c35421687179d21b6e810c750c9b89117 100644 (file)
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -171,8 +171,9 @@ 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 e47a21e64764507d65b04285971c3b34fb327a07..cb08fa65819fc6502cfc6432a34239f88b23d7b9 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3169,6 +3169,9 @@ 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;