From: Khalid Aziz <khalid.aziz@oracle.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: akpm@linux-foundation.org, vbabka@suse.cz,
mgorman@techsingularity.net, dan.j.williams@intel.com,
osalvador@suse.de, richard.weiyang@gmail.com, hannes@cmpxchg.org,
arunks@codeaurora.org, rppt@linux.vnet.ibm.com, jgg@ziepe.ca,
amir73il@gmail.com, alexander.h.duyck@linux.intel.com,
linux-mm@kvack.org,
linux-kernel-mentees@lists.linuxfoundation.org,
linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 0/2] Add predictive memory reclamation and compaction
Date: Tue, 13 Aug 2019 09:20:51 -0600 [thread overview]
Message-ID: <3cb0af00-f091-2f3e-d6cc-73a5171e6eda@oracle.com> (raw)
In-Reply-To: <20190813140553.GK17933@dhcp22.suse.cz>
On 8/13/19 8:05 AM, Michal Hocko wrote:
> On Mon 12-08-19 19:40:10, Khalid Aziz wrote:
> [...]
>> Patch 1 adds code to maintain a sliding lookback window of (time, number
>> of free pages) points which can be updated continuously and adds code to
>> compute best fit line across these points. It also adds code to use the
>> best fit lines to determine if kernel must start reclamation or
>> compaction.
>>
>> Patch 2 adds code to collect data points on free pages of various orders
>> at different points in time, uses code in patch 1 to update sliding
>> lookback window with these points and kicks off reclamation or
>> compaction based upon the results it gets.
>
> An important piece of information missing in your description is why
> do we need to keep that logic in the kernel. In other words, we have
> the background reclaim that acts on a wmark range and those are tunable
> from the userspace. The primary point of this background reclaim is to
> keep balance and prevent from direct reclaim. Why cannot you implement
> this or any other dynamic trend watching watchdog and tune watermarks
> accordingly? Something similar applies to kcompactd although we might be
> lacking a good interface.
>
Hi Michal,
That is a very good question. As a matter of fact the initial prototype
to assess the feasibility of this approach was written in userspace for
a very limited application. We wrote the initial prototype to monitor
fragmentation and used /sys/devices/system/node/node*/compact to trigger
compaction. The prototype demonstrated this approach has merits.
The primary reason to implement this logic in the kernel is to make the
kernel self-tuning. The more knobs we have externally, the more complex
it becomes to tune the kernel externally. If we can make the kernel
self-tuning, we can actually eliminate external knobs and simplify
kernel admin. Inspite of availability of tuning knobs and large number
of tuning guides for databases and cloud platforms, allocation stalls is
a routinely occurring problem on customer deployments. A best fit line
algorithm shows immeasurable impact on system performance yet provides
measurable improvement and room for further refinement. Makes sense?
Thanks,
Khalid
next prev parent reply other threads:[~2019-08-13 15:23 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-13 1:40 [RFC PATCH 0/2] Add predictive memory reclamation and compaction Khalid Aziz
2019-08-13 1:40 ` [RFC PATCH 1/2] mm: Add trend based prediction algorithm for memory usage Khalid Aziz
2019-08-13 1:40 ` [RFC PATCH 2/2] mm/vmscan: Add fragmentation and page starvation prediction to kswapd Khalid Aziz
2019-08-13 14:05 ` [RFC PATCH 0/2] Add predictive memory reclamation and compaction Michal Hocko
2019-08-13 15:20 ` Khalid Aziz [this message]
2019-08-14 8:58 ` Michal Hocko
2019-08-15 16:27 ` Khalid Aziz
2019-08-15 17:02 ` Michal Hocko
2019-08-15 20:51 ` Khalid Aziz
2019-08-21 14:06 ` Michal Hocko
2019-08-26 20:44 ` Bharath Vedartham
2019-08-27 6:16 ` Michal Hocko
2019-08-28 13:09 ` Bharath Vedartham
2019-08-28 13:15 ` Michal Hocko
2019-08-30 21:35 ` Khalid Aziz
2019-09-02 8:02 ` Michal Hocko
2019-09-03 19:45 ` Khalid Aziz
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