mm/mincore: improve performance by adding an unlikely hint

Adding an unlikely() hint on the masked start comparison error return path
improves run-time performance of the mincore system call.

Benchmarking on an i9-12900 shows an improvement of 7ns on mincore calls
on a 256KB mmap'd region where 50% of the pages we resident.  Improvement
was from ~970 ns down to 963 ns, so a small ~0.7% improvement.

Results based on running 20 tests with turbo disabled (to reduce clock
freq turbo changes), with 10 second run per test and comparing the number
of mincores calls per second.  The % standard deviation of the 20 tests
was ~0.10%, so results are reliable.

Link: https://lkml.kernel.org/r/20250219083607.5183-1-colin.i.king@gmail.com
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Cc: Matthew Wilcow <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/mincore.c b/mm/mincore.c
index d6bd19e520fcfb9389e6825eefd72d0b51ad2969..832f29f46767eed1cecf80ab4018985cd32abf32 100644 (file)
--- a/mm/mincore.c
+++ b/mm/mincore.c
@@ -239,7 +239,7 @@ SYSCALL_DEFINE3(mincore, unsigned long, start, size_t, len,
        start = untagged_addr(start);
 
        /* Check the start address: needs to be page-aligned.. */
-       if (start & ~PAGE_MASK)
+       if (unlikely(start & ~PAGE_MASK))
                return -EINVAL;
 
        /* ..and we need to be passed a valid user-space range */