Messages in this thread | | | Subject | Re: [PATCH v7 02/10] mm/memcg: fold lru_lock in lock_page_lru | From | Konstantin Khlebnikov <> | Date | Mon, 13 Jan 2020 12:55:59 +0300 |
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On 13/01/2020 12.45, Alex Shi wrote: > > > 在 2020/1/10 下午4:49, Konstantin Khlebnikov 写道: >> On 25/12/2019 12.04, Alex Shi wrote: >>> From the commit_charge's explanations and mem_cgroup_commit_charge >>> comments, as well as call path when lrucare is ture, The lru_lock is >>> just to guard the task migration(which would be lead to move_account) >>> So it isn't needed when !PageLRU, and better be fold into PageLRU to >>> reduce lock contentions. >>> >>> Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com> >>> Cc: Johannes Weiner <hannes@cmpxchg.org> >>> Cc: Michal Hocko <mhocko@kernel.org> >>> Cc: Matthew Wilcox <willy@infradead.org> >>> Cc: Vladimir Davydov <vdavydov.dev@gmail.com> >>> Cc: Andrew Morton <akpm@linux-foundation.org> >>> Cc: cgroups@vger.kernel.org >>> Cc: linux-mm@kvack.org >>> Cc: linux-kernel@vger.kernel.org >>> --- >>> mm/memcontrol.c | 9 ++++----- >>> 1 file changed, 4 insertions(+), 5 deletions(-) >>> >>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >>> index c5b5f74cfd4d..0ad10caabc3d 100644 >>> --- a/mm/memcontrol.c >>> +++ b/mm/memcontrol.c >>> @@ -2572,12 +2572,11 @@ static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages) >>> static void lock_page_lru(struct page *page, int *isolated) >>> { >>> - pg_data_t *pgdat = page_pgdat(page); >>> - >>> - spin_lock_irq(&pgdat->lru_lock); >>> if (PageLRU(page)) { >>> + pg_data_t *pgdat = page_pgdat(page); >>> struct lruvec *lruvec; >>> + spin_lock_irq(&pgdat->lru_lock); >> >> That's wrong. Here PageLRU must be checked again under lru_lock. > Hi, Konstantin, > > For logical remain, we can get the lock and then release for !PageLRU. > but I still can figure out the problem scenario. Would like to give more hints?
That's trivial race: page could be isolated from lru between
if (PageLRU(page)) and spin_lock_irq(&pgdat->lru_lock);
> > >> >> >> Also I don't like these functions: >> - called lock/unlock but actually also isolates >> - used just once >> - pgdat evaluated twice > > That's right. I will fold these functions into commit_charge. > > Thanks > Alex >
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