From: Andrew Morton <akpm@linux-foundation.org>
To: "Huang, Ying" <ying.huang@intel.com>
Cc: 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>
Subject: Re: [PATCH -mm -v3] mm, swap: Sort swap entries before free
Date: Fri, 7 Apr 2017 14:43:46 -0700 [thread overview]
Message-ID: <20170407144346.b2e5d3c8364767eb2b4118ed@linux-foundation.org> (raw)
In-Reply-To: <20170407064901.25398-1-ying.huang@intel.com>
On Fri, 7 Apr 2017 14:49:01 +0800 "Huang, Ying" <ying.huang@intel.com> wrote:
> To reduce the lock contention of swap_info_struct->lock when freeing
> swap entry. The freed swap entries will be collected in a per-CPU
> buffer firstly, and be really freed later in batch. During the batch
> freeing, if the consecutive swap entries in the per-CPU buffer belongs
> to same swap device, the swap_info_struct->lock needs to be
> acquired/released only once, so that the lock contention could be
> reduced greatly. But if there are multiple swap devices, it is
> possible that the lock may be unnecessarily released/acquired because
> the swap entries belong to the same swap device are non-consecutive in
> the per-CPU buffer.
>
> To solve the issue, the per-CPU buffer is sorted according to the swap
> device before freeing the swap entries. Test shows that the time
> spent by swapcache_free_entries() could be reduced after the patch.
>
> Test the patch via measuring the run time of swap_cache_free_entries()
> during the exit phase of the applications use much swap space. The
> results shows that the average run time of swap_cache_free_entries()
> reduced about 20% after applying the patch.
"20%" is useful info, but it is much better to present the absolute
numbers, please. If it's "20% of one nanosecond" then the patch isn't
very interesting. If it's "20% of 35 seconds" then we know we have
more work to do.
If there is indeed still a significant problem here then perhaps it
would be better to move the percpu swp_entry_t buffer into the
per-device structure swap_info_struct, so it becomes "per cpu, per
device". That way we should be able to reduce contention further.
Or maybe we do something else - it all depends upon the significance of
this problem, which is why a full description of your measurements is
useful.
next prev parent reply other threads:[~2017-04-07 21:43 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-07 6:49 [PATCH -mm -v3] mm, swap: Sort swap entries before free Huang, Ying
2017-04-07 13:05 ` Rik van Riel
2017-04-07 21:43 ` Andrew Morton [this message]
2017-04-11 7:03 ` Huang, Ying
2017-04-14 1:36 ` Huang, Ying
2017-04-18 4:59 ` Minchan Kim
2017-04-19 8:14 ` Huang, Ying
2017-04-20 6:38 ` Minchan Kim
2017-04-20 7:15 ` Huang, Ying
2017-04-21 12:29 ` Huang, Ying
2017-04-21 23:29 ` Tim Chen
2017-04-23 13:16 ` Huang, Ying
2017-04-24 16:03 ` Tim Chen
2017-04-24 4:52 ` Minchan Kim
2017-04-24 6:47 ` Huang, Ying
2017-04-26 12:42 ` Huang, Ying
2017-04-26 20:13 ` Tim Chen
2017-04-27 1:21 ` Huang, Ying
2017-04-27 16:48 ` Tim Chen
2017-04-27 4:35 ` Minchan Kim
2017-04-28 1:09 ` Huang, Ying
2017-04-28 7:42 ` Minchan Kim
2017-04-28 8:05 ` Huang, Ying
2017-04-28 9:00 ` Minchan Kim
2017-04-28 11:48 ` Huang, Ying
2017-04-28 13:35 ` Huang, Ying
2017-05-02 5:02 ` Minchan Kim
2017-05-02 5:35 ` Huang, Ying
2017-05-02 5:48 ` Minchan Kim
2017-05-02 6:08 ` Huang, Ying
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