Currently, all kmem allocations (namely every kmem_cache_alloc, kmalloc,
alloc_kmem_pages call) are accounted to memory cgroup automatically.
Callers have to explicitly opt out if they don't want/need accounting
for some reason. Such a design decision leads to several problems:
- kmalloc users are highly sensitive to failures, many of them
implicitly rely on the fact that kmalloc never fails, while memcg
makes failures quite plausible.
- A lot of objects are shared among different containers by design.
Accounting such objects to one of containers is just unfair.
Moreover, it might lead to pinning a dead memcg along with its kmem
caches, which aren't tiny, which might result in noticeable increase
in memory consumption for no apparent reason in the long run.
- There are tons of short-lived objects. Accounting them to memcg will
only result in slight noise and won't change the overall picture, but
we still have to pay accounting overhead.
For more info, see
- http://lkml.kernel.org/r/20151105144002.GB15111%40dhcp22.suse.cz
- http://lkml.kernel.org/r/20151106090555.GK29259@esperanza
Therefore this patchset switches to the white list policy. Now kmalloc
users have to explicitly opt in by passing __GFP_ACCOUNT flag.
Currently, the list of accounted objects is quite limited and only
includes those allocations that (1) are known to be easily triggered
from userspace and (2) can fail gracefully (for the full list see patch
no. 6) and it still misses many object types. However, accounting only
those objects should be a satisfactory approximation of the behavior we
used to have for most sane workloads.
This patch (of 6):
Revert 499611ed45 ("kernfs: do not account ino_ida allocations
to memcg").
Black-list kmem accounting policy (aka __GFP_NOACCOUNT) turned out to be
fragile and difficult to maintain, because there seem to be many more
allocations that should not be accounted than those that should be.
Besides, false accounting an allocation might result in much worse
consequences than not accounting at all, namely increased memory
consumption due to pinned dead kmem caches.
So it was decided to switch to the white-list policy. This patch reverts
bits introducing the black-list policy. The white-list policy will be
introduced later in the series.
Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Greg Thelen <gthelen@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
b2a209ffa6