Huan Yang <link@xxxxxxxx> writes: > 在 2023/11/10 20:24, Michal Hocko 写道: >> On Fri 10-11-23 11:48:49, Huan Yang wrote: >> [...] >>> Also, When the application enters the foreground, the startup speed >>> may be slower. Also trace show that here are a lot of block I/O. >>> (usually 1000+ IO count and 200+ms IO Time) We usually observe very >>> little block I/O caused by zram refault.(read: 1698.39MB/s, write: >>> 995.109MB/s), usually, it is faster than random disk reads.(read: >>> 48.1907MB/s write: 49.1654MB/s). This test by zram-perf and I change a >>> little to test UFS. >>> >>> Therefore, if the proactive reclamation encounters many file pages, >>> the application may become slow when it is opened. >> OK, this is an interesting information. From the above it seems that >> storage based IO refaults are order of magnitude more expensive than >> swap (zram in this case). That means that the memory reclaim should >> _in general_ prefer anonymous memory reclaim over refaulted page cache, >> right? Or is there any reason why "frozen" applications are any >> different in this case? > Frozen applications mean that the application process is no longer active, > so once its private anonymous page data is swapped out, the anonymous > pages will not be refaulted until the application becomes active again. > > On the contrary, page caches are usually shared. Even if the > application that > first read the file is no longer active, other processes may still > read the file. > Therefore, it is not reasonable to use the proactive reclamation > interface to > reclaim page caches without considering memory pressure. No. Not all page caches are shared. For example, the page caches used for use-once streaming IO. And, they should be reclaimed firstly. So, your solution may work good for your specific use cases, but it's not a general solution. Per my understanding, you want to reclaim only private pages to avoid impact the performance of other applications. Privately mapped anonymous pages is easy to be identified (And I suggest that you can find a way to avoid reclaim shared mapped anonymous pages). There's some heuristics to identify use-once page caches in reclaiming code. Why doesn't it work for your situation? [snip] -- Best Regards, Huang, Ying
