On Tue, Feb 17, 2015 at 02:51:06AM -0800, Omar Sandoval wrote:
Hi,So I didn't realize this until I saw Tetsuo Handa's email to the ext4
As it turns out, running with low memory is a really easy way to shake
out undesirable behavior in Btrfs. This can be especially bad when
considering that a memory limit is really easy to hit in a container
(e.g., by using cgroup memory.limit_in_bytes). Here's a simple script
that can hit several problems:
cgcreate -g memory:enomem
MEM=$((64 * 1024 * 1024))
echo $MEM > /sys/fs/cgroup/memory/enomem/memory.limit_in_bytes
cgexec -g memory:enomem ~/xfstests/ltp/fsstress -p128 -n999999999 -d /mnt/test &
trap "killall fsstress; exit 0" SIGINT SIGTERM
while true; do
cgexec -g memory:enomem python -c '
l = 
Ignoring for now the cases that drop the filesystem into read-only mode
with relatively little fuss, here are a few patches that fix some of the
low-hanging fruit. They apply to Linus' tree as of today.
list (https://urldefense.proofpoint.com/v1/url?u=http://thread.gmane.org/gmane.comp.file-systems.ext4/47855&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=cKCbChRKsMpTX8ybrSkonQ%3D%3D%0A&m=nzG8bjaiVMyWylHxOvTeXimzfSNyukj4%2BAxs0AZ%2FxOI%3D%0A&s=cbd7d48f1866e79f75b88b7f94a394c53d34adfcc1a30a842382f653c978e180), but
it looks like this behavior was exposed by a change to the kernel memory
allocator related to the too-small-to-fail allocation fiasco. To
summarize, Commit 9879de7373fc (mm: page_alloc: embed OOM killing
naturally into allocation slowpath), merged for v3.19-rc7, changed the
behavior of GFP_NOFS allocations which makes it much easier to trigger
allocation failures in filesystems.
This means that Btrfs falls over under memory pressure pretty easily
now, so it might be a good idea to follow the conversation over at
These are bugs regardless of the outcome there, however, so I'd like to
see this patch series merged.