mm: memcontrol: make swap tracking an integral part of memory control

Without swap page tracking, users that are otherwise memory controlled can
easily escape their containment and allocate significant amounts of memory
that they're not being charged for.  That's because swap does readahead,
but without the cgroup records of who owned the page at swapout, readahead
pages don't get charged until somebody actually faults them into their
page table and we can identify an owner task.  This can be maliciously
exploited with MADV_WILLNEED, which triggers arbitrary readahead
allocations without charging the pages.

Make swap swap page tracking an integral part of memcg and remove the
Kconfig options.  In the first place, it was only made configurable to
allow users to save some memory.  But the overhead of tracking cgroup
ownership per swap page is minimal - 2 byte per page, or 512k per 1G of
swap, or 0.04%.  Saving that at the expense of broken containment
semantics is not something we should present as a coequal option.

The swapaccount=0 boot option will continue to exist, and it will
eliminate the page_counter overhead and hide the swap control files, but
it won't disable swap slot ownership tracking.

This patch makes sure we always have the cgroup records at swapin time;
the next patch will fix the actual bug by charging readahead swap pages at
swapin time rather than at fault time.

v2: fix double swap charge bug in cgroup1/cgroup2 code gating

[hannes@cmpxchg.org: fix crash with cgroup_disable=memory]
  Link: http://lkml.kernel.org/r/20200521215855.GB815153@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Alex Shi <alex.shi@linux.alibaba.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Naresh Kamboju <naresh.kamboju@linaro.org>
Link: http://lkml.kernel.org/r/20200508183105.225460-16-hannes@cmpxchg.org
Debugged-by: Hugh Dickins <hughd@google.com>
Debugged-by: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 16 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 74a5ac65644f..ff5a827303dd 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -819,24 +819,9 @@ config MEMCG
 	  Provides control over the memory footprint of tasks in a cgroup.
 
 config MEMCG_SWAP
-	bool "Swap controller"
+	bool
 	depends on MEMCG && SWAP
-	help
-	  Provides control over the swap space consumed by tasks in a cgroup.
-
-config MEMCG_SWAP_ENABLED
-	bool "Swap controller enabled by default"
-	depends on MEMCG_SWAP
 	default y
-	help
-	  Memory Resource Controller Swap Extension comes with its price in
-	  a bigger memory consumption. General purpose distribution kernels
-	  which want to enable the feature but keep it disabled by default
-	  and let the user enable it by swapaccount=1 boot command line
-	  parameter should have this option unselected.
-	  For those who want to have the feature enabled by default should
-	  select this option (if, for some reason, they need to disable it
-	  then swapaccount=0 does the trick).
 
 config MEMCG_KMEM
 	bool