Messages in this thread | | | Date | Mon, 24 Jan 2011 12:34:58 +0100 | From | Johannes Weiner <> | Subject | Re: [PATCH 1/7] memcg : comment, style fixes for recent patch of move_parent |
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On Mon, Jan 24, 2011 at 08:14:22PM +0900, Hiroyuki Kamezawa wrote: > 2011/1/24 Johannes Weiner <hannes@cmpxchg.org>: > > On Mon, Jan 24, 2011 at 07:15:35PM +0900, KAMEZAWA Hiroyuki wrote: > >> On Mon, 24 Jan 2011 11:14:02 +0100 > >> Johannes Weiner <hannes@cmpxchg.org> wrote: > >> > >> > On Fri, Jan 21, 2011 at 03:37:26PM +0900, KAMEZAWA Hiroyuki wrote: > >> > > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> > >> > > > >> > > A fix for 987eba66e0e6aa654d60881a14731a353ee0acb4 > >> > > > >> > > A clean up for mem_cgroup_move_parent(). > >> > > - remove unnecessary initialization of local variable. > >> > > - rename charge_size -> page_size > >> > > - remove unnecessary (wrong) comment. > >> > > > >> > > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> > >> > > --- > >> > > mm/memcontrol.c | 17 +++++++++-------- > >> > > 1 file changed, 9 insertions(+), 8 deletions(-) > >> > > > >> > > Index: mmotm-0107/mm/memcontrol.c > >> > > =================================================================== > >> > > --- mmotm-0107.orig/mm/memcontrol.c > >> > > +++ mmotm-0107/mm/memcontrol.c > >> > > @@ -2265,7 +2265,7 @@ static int mem_cgroup_move_parent(struct > >> > > struct cgroup *cg = child->css.cgroup; > >> > > struct cgroup *pcg = cg->parent; > >> > > struct mem_cgroup *parent; > >> > > - int charge = PAGE_SIZE; > >> > > + int page_size; > >> > > unsigned long flags; > >> > > int ret; > >> > > > >> > > @@ -2278,22 +2278,23 @@ static int mem_cgroup_move_parent(struct > >> > > goto out; > >> > > if (isolate_lru_page(page)) > >> > > goto put; > >> > > - /* The page is isolated from LRU and we have no race with splitting */ > >> > > - charge = PAGE_SIZE << compound_order(page); > >> > > + > >> > > + page_size = PAGE_SIZE << compound_order(page); > >> > > >> > Okay, so you remove the wrong comment, but that does not make the code > >> > right. What protects compound_order from reading garbage because the > >> > page is currently splitting? > >> > > >> > >> == > >> static int mem_cgroup_move_account(struct page_cgroup *pc, > >> struct mem_cgroup *from, struct mem_cgroup *to, > >> bool uncharge, int charge_size) > >> { > >> int ret = -EINVAL; > >> unsigned long flags; > >> > >> if ((charge_size > PAGE_SIZE) && !PageTransHuge(pc->page)) > >> return -EBUSY; > >> == > >> > >> This is called under compound_lock(). Then, if someone breaks THP, > >> -EBUSY and retry. > > > > This charge_size contains exactly the garbage you just read from an > > unprotected compound_order(). It could be anything if the page is > > split concurrently. > > Then, my recent fix to LRU accounting which use compound_order() is racy, too ?
In lru add/delete/move/rotate? No, that should be safe because we have the lru lock there and __split_huge_page_refcount() takes the lock as well.
> I'll replace compound_order() with > if (PageTransHuge(page)) > size = HPAGE_SIZE. > > Does this work ?
Yes, I think this should work. This gives a sane size for try_charge and we still catch a split under the compound_lock later in move_account as you described above. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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