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

[Dave Chinner <david@fromorbit.com>]

On Wed, Jan 22, 2020 at 09:46:57PM +0800, Yafang Shao wrote:
> 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 ?

Sorry, I lost track of this amongst travel and conferences mid
january. Can you update and post it again once -rc1 is out?

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com