KAMEZAWA Hiroyuki wrote:
On Thu, 16 Feb 2012 02:57:04 +0400
Konstantin Khlebnikov<khlebnikov@xxxxxxxxxx> 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:
AFAIK, Hugh Dickins said he has per-zone-per-lru-lock and is testing it.
So, please CC him and Johannes, at least.
Ok
* 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 ]
Why you need to add new structure rahter than enhancing lruvec ?
"book" means a binder of pages ?
I responded to this in the reply to Hugh Dickins.
* 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 ]
This seems straightforward.
* unify inactive_list_is_low_global() and cleanup reclaimer code
* replace struct mem_cgroup_zone with single pointer to struct book
Hm, ok.
* optimize page to book translations, move it upper in the call stack,
replace some struct zone arguments with struct book pointer.
a page->book transrater from patch 2/15
+struct book *page_book(struct page *page)
+{
+ struct mem_cgroup_per_zone *mz;
+ struct page_cgroup *pc;
+
+ if (mem_cgroup_disabled())
+ return&page_zone(page)->book;
+
+ pc = lookup_page_cgroup(page);
+ if (!PageCgroupUsed(pc))
+ return&page_zone(page)->book;
+ /* Ensure pc->mem_cgroup is visible after reading PCG_USED. */
+ smp_rmb();
+ mz = mem_cgroup_zoneinfo(pc->mem_cgroup,
+ page_to_nid(page), page_zonenum(page));
+ return&mz->book;
+}
What happens when pc->mem_cgroup is rewritten by move_account() ?
Where is the guard for lockless access of this ?
Initially this suppose to be protected with lru_lock, in final patch they are protected with rcu.
After final patch all page_book() calls are collected in [__re]lock_page_book[_irq]() functions.
They pick some book reference, lock its lru and recheck page -> book reference in loop till success.
Currently I found there only one potential problem: free_mem_cgroup_per_zone_info() in "mm: memory bookkeeping core"
maybe should call spin_unlock_wait(&zone->lru_lock), because some guy can pick page_book(pfn_to_page(pfn))
and try to isolate this page. But I not sure, how this is possible. In final patch it is totally fixed with rcu.
Thanks,
-Kame
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