在 2023/11/9 17:53, Michal Hocko 写道:
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On Thu 09-11-23 09:56:46, Huan Yang wrote:
在 2023/11/8 22:06, Michal Hocko 写道:
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On Wed 08-11-23 14:58:11, Huan Yang wrote:
In some cases, we need to selectively reclaim file pages or anonymous
pages in an unbalanced manner.
For example, when an application is pushed to the background and frozen,
it may not be opened for a long time, and we can safely reclaim the
application's anonymous pages, but we do not want to touch the file pages.
Could you explain why? And also why do you need to swap out in that
case?
When an application is frozen, it usually means that we predict that
it will not be used for a long time. In order to proactively save some
memory, our strategy will choose to compress the application's private
data into zram. And we will also select some of the cold application
data that we think is in zram and swap it out.
The above operations assume that anonymous pages are private to the
application. After the application is frozen, compressing these pages
into zram can save memory to some extent without worrying about
frequent refaults.
Why don't you rely on the default reclaim heuristics? In other words do
As I mentioned earlier, the madvise approach may not be suitable for my
needs.
you have any numbers showing that a selective reclaim results in a much
In the mobile field, we have a core metric called application residency.
This mechanism can help us improve the application residency if we can
provide
a good freeze detection and proactive reclamation policy.
I can only provide specific data from our internal tests, and it may be
older data,
and it tested using cgroup v1:
In 12G ram phone, app residency improve from 29 to 38.
better behavior? How do you evaluate that?
And the cost of refaults on zram is lower than that of IO.
This patchset extends the proactive reclaim interface to achieve
unbalanced reclamation. Users can control the reclamation tendency by
inputting swappiness under the original interface. Specifically, users
can input special values to extremely reclaim specific pages.
Other have already touched on this in other replies but v2 doesn't have
a per-memcg swappiness
Example:
echo "1G" 200 > memory.reclaim (only reclaim anon)
echo "1G" 0 > memory.reclaim (only reclaim file)
echo "1G" 1 > memory.reclaim (only reclaim file)
Note that when performing unbalanced reclamation, the cgroup swappiness
will be temporarily adjusted dynamically to the input value. Therefore,
if the cgroup swappiness is further modified during runtime, there may
be some errors.
In general this is a bad semantic. The operation shouldn't have side
effect that are potentially visible for another operation.
So, maybe pass swappiness into sc and keep a single reclamation ensure that
swappiness is not changed?
That would be a much saner approach.
Or, it's a bad idea that use swappiness to control unbalance reclaim.
Memory reclaim is not really obliged to consider swappiness. In fact the
actual behavior has changed several times in the past and it is safer to
assume this might change in the future again.
Thank you for the guidance.
--
Michal Hocko
SUSE Labs
--
Thanks,
Huan Yang
