在 2023/11/10 20:32, Michal Hocko 写道:
On Fri 10-11-23 14:21:17, Huan Yang wrote:
[...]
BTW: how do you know the number of pages to be reclaimed proactively in
memcg proactive reclaiming based solution?
One point here is that we are not sure how long the frozen application
will be opened, it could be 10 minutes, an hour, or even days. So we
need to predict and try, gradually reclaim anonymous pages in
proportion, preferably based on the LRU algorithm. For example, if
the application has been frozen for 10 minutes, reclaim 5% of
anonymous pages; 30min:25%anon, 1hour:75%, 1day:100%. It is even more
complicated as it requires adding a mechanism for predicting failure
penalties.
Why would make your reclaiming decisions based on time rather than the
actual memory demand? I can see how a pro-active reclaim could make a
head room for an unexpected memory pressure but applying more pressure
just because of inactivity sound rather dubious to me TBH. Why cannot
you simply wait for the external memory pressure (e.g. from kswapd) to
deal with that based on the demand?
Because the current kswapd and direct memory reclamation are a passive
memory reclamation based on the watermark, and in the event of triggering
these reclamation scenarios, the smoothness of the phone application cannot
be guaranteed. (We often observe that when the above reclamation is
triggered,
there is a delay in the application startup, usually accompanied by
block I/O, and
some concurrency issues caused by lock design.)
To ensure the smoothness of application startup, we have a module in
Android called
LMKD (formerly known as lowmemorykiller). Based on a certain algorithm, LMKD
detects if application startup may be delayed and proactively kills
inactive applications.
(For example, based on factors such as refault IO and swap usage.)
However, this behavior may cause the applications we want to protect to
be killed,
which will result in users having to wait for them to restart when they
are reopened,
which may affect the user experience.(For example, if the user wants to
reopen the
application interface they are working on, or re-enter the order
interface they were viewing.)
Therefore, the above proactive reclamation interface is designed to
compress memory
types with minimal cost for upper-layer applications based on reasonable
strategies,
in order to avoid triggering LMKD or memory reclamation as much as possible,
even if it is not balanced.
--
Thanks,
Huan Yang
