On 08.03.20 05:47, Tyler Sanderson wrote: > Tested-by: Tyler Sanderson <tysand@xxxxxxxxxx> > > Test setup: VM with 16 CPU, 64GB RAM. Running Debian 10. We have a 42 > GB file full of random bytes that we continually cat to /dev/null. > This fills the page cache as the file is read. Meanwhile we trigger > the balloon to inflate, with a target size of 53 GB. This setup causes > the balloon inflation to pressure the page cache as the page cache is > also trying to grow. Afterwards we shrink the balloon back to zero (so > total deflate = total inflate). > > Without patch (kernel 4.19.0-5): > Inflation never reaches the target until we stop the "cat file > > /dev/null" process. Total inflation time was 542 seconds. The longest > period that made no net forward progress was 315 seconds (see attached > graph). > Result of "grep balloon /proc/vmstat" after the test: > balloon_inflate 154828377 > balloon_deflate 154828377 > > With patch (kernel 5.6.0-rc4+): > Total inflation duration was 63 seconds. No deflate-queue activity > occurs when pressuring the page-cache. > Result of "grep balloon /proc/vmstat" after the test: > balloon_inflate 12968539 > balloon_deflate 12968539 > > Conclusion: This patch fixes the issue. In the test it reduced > inflate/deflate activity by 12x, and reduced inflation time by 8.6x. > But more importantly, if we hadn't killed the "grep balloon > /proc/vmstat" process then, without the patch, the inflation process > would never reach the target. > > Attached is a png of a graph showing the problematic behavior without > this patch. It shows deflate-queue activity increasing linearly while > balloon size stays constant over the course of more than 8 minutes of > the test. Thanks a lot for the extended test! -- Thanks, David / dhildenb
