From: Mel Gorman <mgorman@techsingularity.net>
To: "Huang, Ying" <ying.huang@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
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 16:39:08 +0100 [thread overview]
Message-ID: <20160831153908.GA8119@techsingularity.net> (raw)
In-Reply-To: <87oa49m0hn.fsf@yhuang-mobile.sh.intel.com>
On Wed, Aug 31, 2016 at 08:17:24AM -0700, Huang, Ying wrote:
> Mel Gorman <mgorman@techsingularity.net> writes:
>
> > On Tue, Aug 30, 2016 at 10:28:09AM -0700, Huang, Ying wrote:
> >> From: Huang Ying <ying.huang@intel.com>
> >>
> >> File pages use a set of radix tree tags (DIRTY, TOWRITE, WRITEBACK,
> >> etc.) to accelerate finding the pages with a specific tag in the radix
> >> tree during inode writeback. But for anonymous pages in the swap
> >> cache, there is no inode writeback. So there is no need to find the
> >> pages with some writeback tags in the radix tree. It is not necessary
> >> to touch radix tree writeback tags for pages in the swap cache.
> >>
> >> Per Rik van Riel's suggestion, a new flag AS_NO_WRITEBACK_TAGS is
> >> introduced for address spaces which don't need to update the writeback
> >> tags. The flag is set for swap caches. It may be used for DAX file
> >> systems, etc.
> >>
> >> With this patch, the swap out bandwidth improved 22.3% (from ~1.2GB/s to
> >> ~ 1.48GBps) in the vm-scalability swap-w-seq test case with 8 processes.
> >> The test is done on a Xeon E5 v3 system. The swap device used is a RAM
> >> simulated PMEM (persistent memory) device. The improvement comes from
> >> the reduced contention on the swap cache radix tree lock. To test
> >> sequential swapping out, the test case uses 8 processes, which
> >> sequentially allocate and write to the anonymous pages until RAM and
> >> part of the swap device is used up.
> >>
> >> Details of comparison is as follow,
> >>
> >> base base+patch
> >> ---------------- --------------------------
> >> %stddev %change %stddev
> >> \ | \
> >> 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.
>
> Sorry, I don't know whether I understand your words. It is something
> about,
>
> __GFP_BITS_SHIFT == 26
>
> So remainning bits in mapping_flags is 6. And now the latest bit is
> used for the flag introduced in the patch?
>
__GFP_BITS_SHIFT + 5 (AS_NO_WRITEBACK_TAGS) = 31
mapping->flags is a combination of AS and GFP flags so increasing
__GFP_BITS_SHIFT overflows mapping->flags on 32-bit as gfp_t is an
unsigned int.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2016-08-31 15:39 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 [this message]
2016-08-31 15:44 ` Huang, Ying
2016-08-31 21:35 ` Andi Kleen
2016-08-31 21:30 ` Andrew Morton
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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