Re: [PATCH v3 0/3] protect page cache from freeing inode

[Yafang Shao <laoar.shao@gmail.com>]

On Thu, Jan 9, 2020 at 12:04 AM Yafang Shao <laoar.shao@gmail.com> wrote:
>
> On my server there're some running MEMCGs protected by memory.{min, low},
> but I found the usage of these MEMCGs abruptly became very small, which
> were far less than the protect limit. It confused me and finally I
> found that was because of inode stealing.
> Once an inode is freed, all its belonging page caches will be dropped as
> well, no matter how may page caches it has. So if we intend to protect the
> page caches in a memcg, we must protect their host (the inode) first.
> Otherwise the memcg protection can be easily bypassed with freeing inode,
> especially if there're big files in this memcg.
> The inherent mismatch between memcg and inode is a trouble. One inode can
> be shared by different MEMCGs, but it is a very rare case. If an inode is
> shared, its belonging page caches may be charged to different MEMCGs.
> Currently there's no perfect solution to fix this kind of issue, but the
> inode majority-writer ownership switching can help it more or less.
>
> - Changes against v2:
>     1. Seperates memcg patches from this patchset, suggested by Roman.
>        A separate patch is alreay ACKed by Roman, please the MEMCG
>        maintianers help take a look at it[1].
>     2. Improves code around the usage of for_each_mem_cgroup(), suggested
>        by Dave
>     3. Use memcg_low_reclaim passed from scan_control, instead of
>        introducing a new member in struct mem_cgroup.
>     4. Some other code improvement suggested by Dave.
>
>
> - Changes against v1:
> Use the memcg passed from the shrink_control, instead of getting it from
> inode itself, suggested by Dave. That could make the laying better.
>
> [1]
> https://lore.kernel.org/linux-mm/CALOAHbBhPgh3WEuLu2B6e2vj1J8K=gGOyCKzb8tKWmDqFs-rfQ@mail.gmail.com/
>
> Yafang Shao (3):
>   mm, list_lru: make memcg visible to lru walker isolation function
>   mm, shrinker: make memcg low reclaim visible to lru walker isolation
>     function
>   memcg, inode: protect page cache from freeing inode
>
>  fs/inode.c                 | 78 ++++++++++++++++++++++++++++++++++++++++++++--
>  include/linux/memcontrol.h | 21 +++++++++++++
>  include/linux/shrinker.h   |  3 ++
>  mm/list_lru.c              | 47 +++++++++++++++++-----------
>  mm/memcontrol.c            | 15 ---------
>  mm/vmscan.c                | 27 +++++++++-------
>  6 files changed, 143 insertions(+), 48 deletions(-)
>

Dave,  Johannes,

Any comments on this new version ?

Thanks
Yafang