Re: [PATCH RFC 00/15] mm: memory book keeping and lru_locksplitting

[Hugh Dickins]

On Thu, 16 Feb 2012, Konstantin Khlebnikov wrote:

> There should be no logic changes in this patchset, this is only tossing bits around.
> [ This patchset is on top some memcg cleanup/rework patches,
>   which I sent to linux-mm@ today/yesterday ]
> 
> Most of things in this patchset are self-descriptive, so here brief plan:
> 
> * Transmute struct lruvec into struct book. Like real book this struct will
>   store set of pages for one zone. It will be working unit for reclaimer code.
> [ If memcg is disabled in config there will only one book embedded into struct zone ]
> 
> * move page-lru counters to struct book
> [ this adds extra overhead in add_page_to_lru_list()/del_page_from_lru_list() for
>   non-memcg case, but I believe it will be invisible, only one non-atomic add/sub
>   in the same cacheline with lru list ]
> 
> * unify inactive_list_is_low_global() and cleanup reclaimer code
> * replace struct mem_cgroup_zone with single pointer to struct book
> * optimize page to book translations, move it upper in the call stack,
>   replace some struct zone arguments with struct book pointer.
> 
> page -> book dereference become main operation, page (even free) will always
> points to one book in its zone. so page->flags bits may contains direct reference to book.
> Maybe we can replace page_zone(page) with book_zone(page_book(page)), without mem cgroups
> book -> zone dereference will be simple container_of().
> 
> Finally, there appears some new locking primitives for decorating lru_lock splitting logic.
> Final patch actually splits zone->lru_lock into small per-book pieces.

Well done, it looks like you've beaten me by a few days: my per-memcg
per-zone locking patches are now split up and ready, except for the
commit comments and performance numbers to support them.

Or perhaps what we've been doing is orthogonal: I've not glanced beyond
your Subjects yet, but those do look very familiar from my own work -
though we're still using "lruvec"s rather than "book"s.

Anyway, I should be well-placed to review what you've done, and had
better switch away from my own patches to testing and reviewing yours
now, checking if we've caught anything that you're missing.  Or maybe
it'll be worth posting mine anyway, we'll see: I'll look to yours first.

> All this code currently *completely untested*, but seems like it already can work.

Oh, perhaps I'm ahead of you after all :)

> 
> After that, there two options how manage struct book on mem-cgroup create/destroy:
> a) [ currently implemented ] allocate and release by rcu.
>    Thus lock_page_book() will be protected with rcu_read_lock().
> b) allocate and never release struct book, reuse them after rcu grace period.
>    It allows to avoid some rcu_read_lock()/rcu_read_unlock() calls on hot paths.
> 
> 
> Motivation:
> I wrote the similar memory controller for our rhel6-based openvz/virtuozzo kernel,
> including splitted lru-locks and some other [patented LOL] cool stuff.
> [ common descrioption without techical details: http://wiki.openvz.org/VSwap ]
> That kernel already in production and rather stable for a long time.
> 
> ---
> 
> Konstantin Khlebnikov (15):
>       mm: rename struct lruvec into struct book
>       mm: memory bookkeeping core
>       mm: add book->pages_count
>       mm: unify inactive_list_is_low()
>       mm: add book->reclaim_stat
>       mm: kill struct mem_cgroup_zone
>       mm: move page-to-book translation upper
>       mm: introduce book locking primitives
>       mm: handle book relocks on lumpy reclaim
>       mm: handle book relocks in compaction
>       mm: handle book relock in memory controller
>       mm: optimize books in update_page_reclaim_stat()
>       mm: optimize books in pagevec_lru_move_fn()
>       mm: optimize putback for 0-order reclaim
>       mm: split zone->lru_lock
> 
> 
>  include/linux/memcontrol.h |   52 -------
>  include/linux/mm_inline.h  |  222 ++++++++++++++++++++++++++++-
>  include/linux/mmzone.h     |   26 ++-
>  include/linux/swap.h       |    2 
>  init/Kconfig               |    4 +
>  mm/compaction.c            |   35 +++--
>  mm/huge_memory.c           |   10 +
>  mm/memcontrol.c            |  238 ++++++++++---------------------
>  mm/page_alloc.c            |   20 ++-
>  mm/swap.c                  |  128 ++++++-----------
>  mm/vmscan.c                |  334 +++++++++++++++++++-------------------------
>  11 files changed, 554 insertions(+), 517 deletions(-)

That's a very familiar list of files to me!

Hugh
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