Re: [PATCH v1 0/7] mm/memcontrol: recharge mlocked pages
From: Michal Hocko
Date: Wed Sep 04 2019 - 10:37:51 EST
On Wed 04-09-19 16:53:08, Konstantin Khlebnikov wrote:
> Currently mlock keeps pages in cgroups where they were accounted.
> This way one container could affect another if they share file cache.
> Typical case is writing (downloading) file in one container and then
> locking in another. After that first container cannot get rid of cache.
> Also removed cgroup stays pinned by these mlocked pages.
> This patchset implements recharging pages to cgroup of mlock user.
> There are three cases:
> * recharging at first mlock
> * recharging at munlock to any remaining mlock
> * recharging at 'culling' in reclaimer to any existing mlock
> To keep things simple recharging ignores memory limit. After that memory
> usage temporary could be higher than limit but cgroup will reclaim memory
> later or trigger oom, which is valid outcome when somebody mlock too much.
I assume that this is mlock specific because the pagecache which has the
same problem is reclaimable and the problem tends to resolve itself
after some time.
Anyway, how big of a problem this really is? A lingering memcg is
certainly not nice but pages are usually not mlocked for ever. Or is
this a way to protect from an hostile actor?
> Konstantin Khlebnikov (7):
> mm/memcontrol: move locking page out of mem_cgroup_move_account
> mm/memcontrol: add mem_cgroup_recharge
> mm/mlock: add vma argument for mlock_vma_page()
> mm/mlock: recharge memory accounting to first mlock user
> mm/mlock: recharge memory accounting to second mlock user at munlock
> mm/vmscan: allow changing page memory cgroup during reclaim
> mm/mlock: recharge mlocked pages at culling by vmscan
> Documentation/admin-guide/cgroup-v1/memory.rst | 5 +
> include/linux/memcontrol.h | 9 ++
> include/linux/rmap.h | 3 -
> mm/gup.c | 2
> mm/huge_memory.c | 4 -
> mm/internal.h | 6 +
> mm/ksm.c | 2
> mm/memcontrol.c | 104 ++++++++++++++++--------
> mm/migrate.c | 2
> mm/mlock.c | 14 +++
> mm/rmap.c | 5 +
> mm/vmscan.c | 17 ++--
> 12 files changed, 121 insertions(+), 52 deletions(-)