On Fri 17-03-17 21:08:31, Gerhard Wiesinger wrote: > On 17.03.2017 18:13, Michal Hocko wrote: > >On Fri 17-03-17 17:37:48, Gerhard Wiesinger wrote: > >[...] > >>Why does the kernel prefer to swapin/out and not use > >> > >>a.) the free memory? > >It will use all the free memory up to min watermark which is set up > >based on min_free_kbytes. > > Makes sense, how is /proc/sys/vm/min_free_kbytes default value calculated? See init_per_zone_wmark_min > >>b.) the buffer/cache? > >the memory reclaim is strongly biased towards page cache and we try to > >avoid swapout as much as possible (see get_scan_count). > > If I understand it correctly, swapping is preferred over dropping the > cache, right. Can this behaviour be changed to prefer dropping the > cache to some minimum amount? Is this also configurable in a way? No, we enforce swapping if the amount of free + file pages are below the cumulative high watermark. > (As far as I remember e.g. kernel 2.4 dropped the caches well). > > >>There is ~100M memory available but kernel swaps all the time ... > >> > >>Any ideas? > >> > >>Kernel: 4.9.14-200.fc25.x86_64 > >> > >>top - 17:33:43 up 28 min, 3 users, load average: 3.58, 1.67, 0.89 > >>Tasks: 145 total, 4 running, 141 sleeping, 0 stopped, 0 zombie > >>%Cpu(s): 19.1 us, 56.2 sy, 0.0 ni, 4.3 id, 13.4 wa, 2.0 hi, 0.3 si, 4.7 > >>st > >>KiB Mem : 230076 total, 61508 free, 123472 used, 45096 buff/cache > >> > >>procs -----------memory---------- ---swap-- -----io---- -system-- > >>------cpu----- > >> r b swpd free buff cache si so bi bo in cs us sy id wa st > >> 3 5 303916 60372 328 43864 27828 200 41420 236 6984 11138 11 47 6 23 14 > >I am really surprised to see any reclaim at all. 26% of free memory > >doesn't sound as if we should do a reclaim at all. Do you have an > >unusual configuration of /proc/sys/vm/min_free_kbytes ? Or is there > >anything running inside a memory cgroup with a small limit? > > nothing special set regarding /proc/sys/vm/min_free_kbytes (default values), > detailed config below. Regarding cgroups, none of I know. How to check (I > guess nothing is set because cg* commands are not available)? be careful because systemd started to use some controllers. You can easily check cgroup mount points. > /proc/sys/vm/min_free_kbytes > 45056 So at least 45M will be kept reserved for the system. Your data indicated you had more memory. How does /proc/zoneinfo look like? Btw. you seem to be using fc kernel, are there any patches applied on top of Linus tree? Could you try to retest vanilla kernel? -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
