On Wed, 31 Aug 2016 10:14:59 +0100 Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote:
> > 2506952 __ 2% +28.1% 3212076 __ 7% vm-scalability.throughput
> > 1207402 __ 7% +22.3% 1476578 __ 6% vmstat.swap.so
> > 10.86 __ 12% -23.4% 8.31 __ 16% perf-profile.cycles-pp._raw_spin_lock_irq.__add_to_swap_cache.add_to_swap_cache.add_to_swap.shrink_page_list
> > 10.82 __ 13% -33.1% 7.24 __ 14% perf-profile.cycles-pp._raw_spin_lock_irqsave.__remove_mapping.shrink_page_list.shrink_inactive_list.shrink_zone_memcg
> > 10.36 __ 11% -100.0% 0.00 __ -1% perf-profile.cycles-pp._raw_spin_lock_irqsave.__test_set_page_writeback.bdev_write_page.__swap_writepage.swap_writepage
> > 10.52 __ 12% -100.0% 0.00 __ -1% perf-profile.cycles-pp._raw_spin_lock_irqsave.test_clear_page_writeback.end_page_writeback.page_endio.pmem_rw_page
> >
>
> I didn't see anything wrong with the patch but it's worth highlighting
> that this hunk means we are now out of GFP bits.
Well ugh. What are we to do about that?
Sigh. This?
From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Subject: mm: check that we haven't used more than 32 bits in address_space.flags
After "mm: don't use radix tree writeback tags for pages in swap cache",
all the flags are now used up on 32-bit builds.
Add a build-time assertion to prevent 64-bit developers from accidentally
breaking things.
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/pagemap.h | 2 ++
init/main.c | 4 ++++
2 files changed, 6 insertions(+)
diff -puN include/linux/pagemap.h~mm-check-that-we-havent-used-more-than-32-bits-in-address_spaceflags include/linux/pagemap.h
--- a/include/linux/pagemap.h~mm-check-that-we-havent-used-more-than-32-bits-in-address_spaceflags
+++ a/include/linux/pagemap.h
@@ -27,6 +27,8 @@ enum mapping_flags {
AS_EXITING = __GFP_BITS_SHIFT + 4, /* final truncate in progress */
/* writeback related tags are not used */
AS_NO_WRITEBACK_TAGS = __GFP_BITS_SHIFT + 5,
+
+ AS_LAST_FLAG,
};
static inline void mapping_set_error(struct address_space *mapping, int error)
diff -puN init/main.c~mm-check-that-we-havent-used-more-than-32-bits-in-address_spaceflags init/main.c
--- a/init/main.c~mm-check-that-we-havent-used-more-than-32-bits-in-address_spaceflags
+++ a/init/main.c
@@ -59,6 +59,7 @@
#include <linux/pid_namespace.h>
#include <linux/device.h>
#include <linux/kthread.h>
+#include <linux/pagemap.h>
#include <linux/sched.h>
#include <linux/signal.h>
#include <linux/idr.h>
@@ -463,6 +464,9 @@ void __init __weak thread_stack_cache_in
*/
static void __init mm_init(void)
{
+ /* Does address_space.flags still fit into a 32-bit ulong? */
+ BUILD_BUG_ON(AS_LAST_FLAG > 32);
+
/*
* page_ext requires contiguous pages,
* bigger than MAX_ORDER unless SPARSEMEM.
_
--
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