From: Andrew Morton <akpm@linux-foundation.org>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: "Huang, Ying" <ying.huang@intel.com>,
tim.c.chen@intel.com, dave.hansen@intel.com,
andi.kleen@intel.com, aaron.lu@intel.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, Hugh Dickins <hughd@google.com>,
Shaohua Li <shli@kernel.org>, Minchan Kim <minchan@kernel.org>,
Rik van Riel <riel@redhat.com>, Tejun Heo <tj@kernel.org>,
Wu Fengguang <fengguang.wu@intel.com>
Subject: Re: [PATCH -v2] mm: Don't use radix tree writeback tags for pages in swap cache
Date: Wed, 31 Aug 2016 14:30:31 -0700 [thread overview]
Message-ID: <20160831143031.4e5a180f969ec6997637a96f@linux-foundation.org> (raw)
In-Reply-To: <20160831091459.GY8119@techsingularity.net>
On Wed, 31 Aug 2016 10:14:59 +0100 Mel Gorman <mgorman@techsingularity.net> 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@linux-foundation.org>
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@techsingularity.net>
Cc: "Huang, Ying" <ying.huang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
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.
_
next prev parent reply other threads:[~2016-08-31 21:30 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-30 17:28 [PATCH -v2] mm: Don't use radix tree writeback tags for pages in swap cache Huang, Ying
2016-08-30 18:29 ` Rik van Riel
2016-08-31 9:14 ` Mel Gorman
2016-08-31 15:17 ` Huang, Ying
2016-08-31 15:39 ` Mel Gorman
2016-08-31 15:44 ` Huang, Ying
2016-08-31 21:35 ` Andi Kleen
2016-08-31 21:30 ` Andrew Morton [this message]
2016-09-01 8:51 ` Mel Gorman
2016-09-01 9:13 ` Michal Hocko
2016-09-12 11:16 ` [PATCH 0/2] do not squash mapping flags and gfp_mask together (was: Re: [PATCH -v2] mm: Don't use radix tree writeback tags for pages in) Michal Hocko
2016-09-12 11:16 ` [PATCH 1/2] fs: use mapping_set_error instead of opencoded set_bit Michal Hocko
2016-09-12 22:11 ` Andrew Morton
2016-09-12 22:18 ` Andrew Morton
2016-09-13 6:53 ` Michal Hocko
2016-09-13 21:29 ` Andrew Morton
2016-09-12 11:16 ` [PATCH 2/2] mm: split gfp_mask and mapping flags into separate fields Michal Hocko
2016-09-12 11:48 ` Michal Hocko
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