On 06/18/2017 04:21 PM, Jens Axboe wrote: > On 06/18/2017 10:30 AM, Jeff Layton wrote: >> I've run across a regression from v4.11. If I boot a v4.12-rc1 or later >> kernel, make a large brd device and try to format it, it quickly slows >> down to a crawl and then the OOM killer kicks in. >> >> I ran a bisect and it landed here: >> >> commit f09a06a193d942a12c1a33c153388b3962222006 (HEAD, refs/bisect/bad) >> Author: Christoph Hellwig <h...@lst.de> >> Date: Wed Apr 5 19:21:16 2017 +0200 >> >> brd: remove discard support >> >> It's just a in-driver reimplementation of writing zeroes to the pages, >> which fails if the discards aren't page aligned. >> >> Signed-off-by: Christoph Hellwig <h...@lst.de> >> Reviewed-by: Hannes Reinecke <h...@suse.com> >> Signed-off-by: Jens Axboe <ax...@fb.com> >> >> >> I've been reproducing it in a VM with ~8G allocated to it: >> >> I have a modprobe.d file with this in it: >> >> options brd rd_nr=1 rd_size=1073741824 >> >> I then just: >> >> # modprobe brd >> # mkfs -t ext2 /dev/ram0 >> >> It keels over pretty quickly after that. > > Just checked, and creating a 1TB ram disk and then running mkfs.ext2 on it > writes 16851MiB of data. I can't say I'm surprised you OOM, if you run that > in a 8G VM, as you're about 8G short. > > I'm puzzled as to why the discard change would make any difference, however.
Reverted the patch, and I see identical behavior. The only difference is that the whole device is trimmed first, as expected. But it still writes ~16G afterwards. Are you sure this commit is what broke things for you? Honestly, I don't see how it could ever work with 1TB ram disk, 8G of RAM, and 16G of data written. -- Jens Axboe
