| Message ID | 20200420223936.6773-1-schatzberg.dan@gmail.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Charge loop device i/o to issuing cgroup | expand |
On Tue, Apr 21, 2020 at 10:48:45AM +0800, Hillf Danton wrote: > > On Mon, 20 Apr 2020 18:39:29 -0400 Dan Schatzberg wrote: > > > > @@ -1140,8 +1215,17 @@ static int __loop_clr_fd(struct loop_device *lo, bool release) > > blk_mq_freeze_queue(lo->lo_queue); > > > > spin_lock_irq(&lo->lo_lock); > > + destroy_workqueue(lo->workqueue); > > Destruct it out of atomic context. I may as well do this, but it doesn't matter, does it? The blk_mq_freeze_queue above should drain all I/O so the workqueue will be idle.
On Tue, Apr 21, 2020 at 11:33:37AM +0800, Hillf Danton wrote: > > On Mon, 20 Apr 2020 18:39:32 -0400 Dan Schatzberg wrote: > > > > @@ -964,13 +960,16 @@ static void loop_queue_work(struct loop_device *lo, struct loop_cmd *cmd) > > worker = kzalloc(sizeof(struct loop_worker), GFP_NOWAIT | __GFP_NOWARN); > > /* > > * In the event we cannot allocate a worker, just queue on the > > - * rootcg worker > > + * rootcg worker and issue the I/O as the rootcg > > */ > > - if (!worker) > > + if (!worker) { > > + cmd->blkcg_css = NULL; > > + cmd->memcg_css = NULL; > > Dunno if css_put(cmd->memcg_css); Good catch. Need to drop the reference here.
Changes since V4: Only patches 1 and 2 have changed. * Fixed irq lock ordering bug * Simplified loop detach * Added support for nesting memalloc_use_memcg Changes since V3: * Fix race on loop device destruction and deferred worker cleanup * Ensure charge on shmem_swapin_page works just like getpage * Minor style changes Changes since V2: * Deferred destruction of workqueue items so in the common case there is no allocation needed Changes since V1: * Split out and reordered patches so cgroup charging changes are separate from kworker -> workqueue change * Add mem_css to struct loop_cmd to simplify logic The loop device runs all i/o to the backing file on a separate kworker thread which results in all i/o being charged to the root cgroup. This allows a loop device to be used to trivially bypass resource limits and other policy. This patch series fixes this gap in accounting. A simple script to demonstrate this behavior on cgroupv2 machine: ''' #!/bin/bash set -e CGROUP=/sys/fs/cgroup/test.slice LOOP_DEV=/dev/loop0 if [[ ! -d $CGROUP ]] then sudo mkdir $CGROUP fi grep oom_kill $CGROUP/memory.events # Set a memory limit, write more than that limit to tmpfs -> OOM kill sudo unshare -m bash -c " echo \$\$ > $CGROUP/cgroup.procs; echo 0 > $CGROUP/memory.swap.max; echo 64M > $CGROUP/memory.max; mount -t tmpfs -o size=512m tmpfs /tmp; dd if=/dev/zero of=/tmp/file bs=1M count=256" || true grep oom_kill $CGROUP/memory.events # Set a memory limit, write more than that limit through loopback # device -> no OOM kill sudo unshare -m bash -c " echo \$\$ > $CGROUP/cgroup.procs; echo 0 > $CGROUP/memory.swap.max; echo 64M > $CGROUP/memory.max; mount -t tmpfs -o size=512m tmpfs /tmp; truncate -s 512m /tmp/backing_file losetup $LOOP_DEV /tmp/backing_file dd if=/dev/zero of=$LOOP_DEV bs=1M count=256; losetup -D $LOOP_DEV" || true grep oom_kill $CGROUP/memory.events ''' Naively charging cgroups could result in priority inversions through the single kworker thread in the case where multiple cgroups are reading/writing to the same loop device. This patch series does some minor modification to the loop driver so that each cgroup can make forward progress independently to avoid this inversion. With this patch series applied, the above script triggers OOM kills when writing through the loop device as expected. Dan Schatzberg (4): loop: Use worker per cgroup instead of kworker mm: support nesting memalloc_use_memcg() mm: Charge active memcg when no mm is set loop: Charge i/o to mem and blk cg drivers/block/loop.c | 246 ++++++++++++++++++++++----- drivers/block/loop.h | 14 +- fs/buffer.c | 6 +- fs/notify/fanotify/fanotify.c | 5 +- fs/notify/inotify/inotify_fsnotify.c | 5 +- include/linux/memcontrol.h | 6 + include/linux/sched/mm.h | 28 +-- kernel/cgroup/cgroup.c | 1 + mm/memcontrol.c | 11 +- mm/shmem.c | 4 +- 10 files changed, 246 insertions(+), 80 deletions(-)