On 02/22/2018 05:09 PM, Michal Hocko wrote: > On Thu 22-02-18 16:50:33, Andrey Ryabinin wrote: >> On 02/21/2018 11:17 PM, Andrew Morton wrote: >>> On Fri, 19 Jan 2018 16:11:18 +0100 Michal Hocko <mhocko@xxxxxxxxxx> wrote: >>> >>>> And to be honest, I do not really see why keeping retrying from >>>> mem_cgroup_resize_limit should be so much faster than keep retrying from >>>> the direct reclaim path. We are doing SWAP_CLUSTER_MAX batches anyway. >>>> mem_cgroup_resize_limit loop adds _some_ overhead but I am not really >>>> sure why it should be that large. >>> >>> Maybe restarting the scan lots of times results in rescanning lots of >>> ineligible pages at the start of the list before doing useful work? >>> >>> Andrey, are you able to determine where all that CPU time is being spent? >>> >> >> I should have been more specific about the test I did. The full script looks like this: >> >> mkdir -p /sys/fs/cgroup/memory/test >> echo $$ > /sys/fs/cgroup/memory/test/tasks >> cat 4G_file > /dev/null >> while true; do cat 4G_file > /dev/null; done & >> loop_pid=$! >> perf stat echo 50M > /sys/fs/cgroup/memory/test/memory.limit_in_bytes >> echo -1 > /sys/fs/cgroup/memory/test/memory.limit_in_bytes >> kill $loop_pid >> >> >> I think the additional loops add some overhead and it's not that big by itself, but >> this small overhead allows task to refill slightly more pages, increasing >> the total amount of pages that mem_cgroup_resize_limit() need to reclaim. >> >> By using the following commands to show the the amount of reclaimed pages: >> perf record -e vmscan:mm_vmscan_memcg_reclaim_end echo 50M > /sys/fs/cgroup/memory/test/memory.limit_in_bytes >> perf script|cut -d '=' -f 2| paste -sd+ |bc >> >> I've got 1259841 pages (4.9G) with the patch vs 1394312 pages (5.4G) without it. > > So how does the picture changes if you have multiple producers? > Drastically, in favor of the patch. But numbers *very* fickle from run to run. Inside 5G vm with 4 cpus (qemu -m 5G -smp 4) and 4 processes in cgroup reading 1G files: "while true; do cat /1g_f$i > /dev/null; done &" with the patch: best: 1.04 secs, 9.7G reclaimed worst: 2.2 secs, 16G reclaimed. without: best: 5.4 sec, 35G reclaimed worst: 22.2 sec, 136G reclaimed -- 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>
