On 2018/11/14 下午2:47, Nikolay Borisov wrote: > > > On 14.11.18 г. 2:31 ч., Qu Wenruo wrote: >> Hi, >> >> Is there any (easy) method for a fstests test case to limit the page >> cache usage? >> >> I triggered btrfs/139 failure with 2G vRAM VM, and located the root >> cause of the problem. > > You can always size your test vm properly. Otherwise what about the > various sysctl tuning knobs? I.e Documentation/sysctl/vm.txt explains > some of them: dirty_bytes, dirty_background_bytes, > dirty_background_ratio, dirty_expire_centisecs Thanks for the hint about vm.txt! I just realized we could just drop_caches to force dirty page writeback, without the need to tweaking the complex memory pressure/watermark mechanism. Thanks, Qu > > > So with a 2g machine the default settings are using only a fraction of > the ram. If you adjust the same settings for the larger ram size you > should get almost identical behavior.> > > >> >> However it's only really reproducible for small ram VM, since it could >> trigger dirty page writeback due to memory pressure. >> >> So I'm wondering if we could do such thing even for large RAM test machine. >> >> Thanks, >> Qu >>
