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authorHugh Dickins <hughd@google.com>2010-09-09 16:38:11 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-09-09 18:57:25 -0700
commit3399446632739fcd05fd8b272b476a69c6e6d14a (patch)
tree986d5b880aa69a16c8f3a6bded68cb50f9418d29 /mm
parent8f2ae0faa3a119158c4dcfe89926d6fad5f5332c (diff)
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swap: discard while swapping only if SWAP_FLAG_DISCARD
Tests with recent firmware on Intel X25-M 80GB and OCZ Vertex 60GB SSDs show a shift since I last tested in December: in part because of firmware updates, in part because of the necessary move from barriers to awaiting completion at the block layer. While discard at swapon still shows as slightly beneficial on both, discarding 1MB swap cluster when allocating is now disadvanteous: adds 25% overhead on Intel, adds 230% on OCZ (YMMV). Surrender: discard as presently implemented is more hindrance than help for swap; but might prove useful on other devices, or with improvements. So continue to do the discard at swapon, but make discard while swapping conditional on a SWAP_FLAG_DISCARD to sys_swapon() (which has been using only the lower 16 bits of int flags). We can add a --discard or -d to swapon(8), and a "discard" to swap in /etc/fstab: matching the mount option for btrfs, ext4, fat, gfs2, nilfs2. Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Nigel Cunningham <nigel@tuxonice.net> Cc: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <jaxboe@fusionio.com> Cc: James Bottomley <James.Bottomley@hansenpartnership.com> Cc: "Martin K. Petersen" <martin.petersen@oracle.com> Cc: <stable@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/swapfile.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 1894dead0b5..7c703ff2f36 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2047,7 +2047,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
p->flags |= SWP_SOLIDSTATE;
p->cluster_next = 1 + (random32() % p->highest_bit);
}
- if (discard_swap(p) == 0)
+ if (discard_swap(p) == 0 && (swap_flags & SWAP_FLAG_DISCARD))
p->flags |= SWP_DISCARDABLE;
}