[PATCH 00/18] mm: memcontrol: charge swapin pages on instantiation

Johannes Weiner
2020-04-20T22:11:40Z

This patch series reworks memcg to charge swapin pages directly at
swapin time, rather than at fault time, which may be much later, or
not happen at all.

The delayed charging scheme we have right now causes problems:

- Alex's per-cgroup lru_lock patches rely on pages that have been
isolated from the LRU to have a stable page->mem_cgroup; otherwise
the lock may change underneath him. Swapcache pages are charged only
after they are added to the LRU, and charging doesn't follow the LRU
isolation protocol.

- Joonsoo's anon workingset patches need a suitable LRU at the time
the page enters the swap cache and displaces the non-resident
info. But the correct LRU is only available after charging.

- It's a containment hole / DoS vector. Users can trigger arbitrarily
large swap readahead using MADV_WILLNEED. The memory is never
charged unless somebody actually touches it.

- It complicates the page->mem_cgroup stabilization rules

In order to charge pages directly at swapin time, the memcg code base
needs to be prepared, and several overdue cleanups become a necessity:

To charge pages at swapin time, we need to always have cgroup
ownership tracking of swap records. We also cannot rely on
page->mapping to tell apart page types at charge time, because that's
only set up during a page fault.

To eliminate the page->mapping dependency, memcg needs to ditch its
private page type counters (MEMCG_CACHE, MEMCG_RSS, NR_SHMEM) in favor
of the generic vmstat counters and accounting sites, such as
NR_FILE_PAGES, NR_ANON_MAPPED etc.

To switch to generic vmstat counters, the charge sequence must be
adjusted such that page->mem_cgroup is set up by the time these
counters are modified.

The series is structured as follows:

1. Bug fixes
2. Decoupling charging from rmap
3. Swap controller integration into memcg
4. Direct swapin charging

The patches survive a simple swapout->swapin test inside a virtual
machine. Because this is blocking two major patch sets, I'm sending
these out early and will continue testing in parallel to the review.

include/linux/memcontrol.h | 53 +----
include/linux/mm.h | 4 +-
include/linux/swap.h | 6 +-
init/Kconfig | 17 +-
kernel/events/uprobes.c | 10 +-
mm/filemap.c | 43 ++---
mm/huge_memory.c | 45 ++---
mm/khugepaged.c | 25 +--
mm/memcontrol.c | 448 ++++++++++++++-----------------------------
mm/memory.c | 51 ++---
mm/migrate.c | 20 +-
mm/rmap.c | 53 +++--
mm/shmem.c | 117 +++++------
mm/swap_cgroup.c | 6 -
mm/swap_state.c | 89 +++++----
mm/swapfile.c | 25 +--
mm/userfaultfd.c | 5 +-
17 files changed, 367 insertions(+), 650 deletions(-)