Messages in this thread | | | Subject | Re: Detecting page cache trashing state | From | Zdenek Kabelac <> | Date | Fri, 15 Sep 2017 13:55:37 +0200 |
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Dne 15.9.2017 v 02:16 Taras Kondratiuk napsal(a): > Hi > > In our devices under low memory conditions we often get into a trashing > state when system spends most of the time re-reading pages of .text > sections from a file system (squashfs in our case). Working set doesn't > fit into available page cache, so it is expected. The issue is that > OOM killer doesn't get triggered because there is still memory for > reclaiming. System may stuck in this state for a quite some time and > usually dies because of watchdogs. > > We are trying to detect such trashing state early to take some > preventive actions. It should be a pretty common issue, but for now we > haven't find any existing VM/IO statistics that can reliably detect such > state. > > Most of metrics provide absolute values: number/rate of page faults, > rate of IO operations, number of stolen pages, etc. For a specific > device configuration we can determine threshold values for those > parameters that will detect trashing state, but it is not feasible for > hundreds of device configurations. > > We are looking for some relative metric like "percent of CPU time spent > handling major page faults". With such relative metric we could use a > common threshold across all devices. For now we have added such metric > to /proc/stat in our kernel, but we would like to find some mechanism > available in upstream kernel. > > Has somebody faced similar issue? How are you solving it? > Hi
Well I witness this when running Firefox & Thunderbird on my desktop for a while on just 4G RAM machine till these 2app eat all free RAM...
It gets to the position (when I open new tab) that mouse hardly moves - kswapd eats CPU (I've no swap in fact - so likely just page-caching).
The only 'quick' solution for me as desktop user is to manually invoke OOM with SYSRQ+F key - and I'm also wondering why the system is not reacting better. In most cases it kills one of those 2 - but sometime it kills whole Xsession...
Regards
Zdenek
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