On 2018/11/14 下午3:00, Qu Wenruo wrote: > > > 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. Well, this doesn't work as expected. It will cause transaction commit, seems that kernel is trying too hard to free page cache. Is there any way to only flush dirty pages of a file? Thanks, Qu > > 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 >>>
