Re: [PATCH V2 0/3] memcg: simply lock of page stat accounting

[Konstantin Khlebnikov <khlebnikov@openvz.org>]

Sha Zhengju wrote:
> Hi,
>
> This is my second attempt to make memcg page stat lock simpler, the
> first version: http://www.spinics.net/lists/linux-mm/msg50037.html.
>
> In this version I investigate the potential race conditions among
> page stat, move_account, charge, uncharge and try to prove it race
> safe of my proposing lock scheme. The first patch is the basis of
> the patchset, so if I've made some stupid mistake please do not
> hesitate to point it out.

I have a provocational question. Who needs these numbers? I mean per-cgroup
nr_mapped and so on. It's too hard to maintain them carefully and I don't know
any clear usage for them. I have written several implementations of this stuff
for openvz kernel. But at the end I have decided to just remove it.
Do anybody knows really useful use cases for these nr_mapped counters?


In our kernel we have per-container nr_dirty and nr_writeback counters. Bit they are
implemented on top of radix-tree tags, and their owners are stored on inode/mapping.
So, this is completely different story.

I definitely have missed some discussions about these questions. Or not?
I hope it's a good time to return.

>
> Change log:
> v2<- v1:
>     * rewrite comments on race condition
>     * split orignal large patch to two parts
>     * change too heavy try_get_mem_cgroup_from_page() to rcu_read_lock
>       to hold memcg alive
>
> Sha Zhengju (3):
>     memcg: rewrite the comment about race condition of page stat accounting
>     memcg: alter mem_cgroup_{update,inc,dec}_page_stat() args to memcg pointer
>     memcg: simplify lock of memcg page stat account	
>
>   include/linux/memcontrol.h |   14 ++++++-------
>   mm/memcontrol.c            |   16 ++++++---------
>   mm/rmap.c                  |   49 +++++++++++++++++++++++++++++++++-----------
>   3 files changed, 50 insertions(+), 29 deletions(-)
>
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