mm/swap: fix kernel message in swap_info_get()

Patch series "mm/swap: Regular page swap optimizations", v5.

Times have changed.  Coming generation of Solid state Block device
latencies are getting down to sub 100 usec, which is within an order of
magnitude of DRAM, and their performance is orders of magnitude higher
than the single- spindle rotational media we've swapped to historically.

This could benefit many usage scenearios.  For example cloud providers
who overcommit their memory (as VM don't use all the memory
provisioned).  Having a fast swap will allow them to be more aggressive
in memory overcommit and fit more VMs to a platform.

In our testing [see footnote], the median latency that the kernel adds
to a page fault is 15 usec, which comes quite close to the amount that
will be contributed by the underlying I/O devices.

The software latency comes mostly from contentions on the locks
protecting the radix tree of the swap cache and also the locks
protecting the individual swap devices.  The lock contentions already
consumed 35% of cpu cycles in our test.  In the very near future,
software latency will become the bottleneck to swap performnace as block
device I/O latency gets within the shouting distance of DRAM speed.

This patch set, reduced the median page fault latency from 15 usec to 4
usec (375% reduction) for DRAM based pmem block device.

This patch (of 9):

swap_info_get() is used not only in swap free code path but also in
page_swapcount(), etc.  So the original kernel message in swap_info_get()
is not correct now.  Fix it via replacing "swap_free" to "swap_info_get"
in the message.

Link: http://lkml.kernel.org/r/9b5f8bd6266f9da978c373f2384c8044df5e262c.1484082593.git.tim.c.chen@linux.intel.com
Signed-off-by: "Huang, Ying" <[email protected]>
Signed-off-by: Tim Chen <[email protected]>
Reviewed-by: Rik van Riel <[email protected]>
Cc: Aaron Lu <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Christian Borntraeger <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Hillf Danton <[email protected]>
Cc: Huang Ying <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Jonathan Corbet <[email protected]> escreveu:
Cc: Kirill A. Shutemov <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Shaohua Li <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/swapfile.c

@@ -753,16 +753,16 @@ static struct swap_info_struct *swap_info_get(swp_entry_t entry)
 	return p;
 
 bad_free:
-	pr_err("swap_free: %s%08lx\n", Unused_offset, entry.val);
+	pr_err("swap_info_get: %s%08lx\n", Unused_offset, entry.val);
 	goto out;
 bad_offset:
-	pr_err("swap_free: %s%08lx\n", Bad_offset, entry.val);
+	pr_err("swap_info_get: %s%08lx\n", Bad_offset, entry.val);
 	goto out;
 bad_device:
-	pr_err("swap_free: %s%08lx\n", Unused_file, entry.val);
+	pr_err("swap_info_get: %s%08lx\n", Unused_file, entry.val);
 	goto out;
 bad_nofile:
-	pr_err("swap_free: %s%08lx\n", Bad_file, entry.val);
+	pr_err("swap_info_get: %s%08lx\n", Bad_file, entry.val);
 out:
 	return NULL;
 }