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SubjectRe: [PATCH 03/14] lru/memcg: using per lruvec lock in un/lock_page_lru
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On 20/08/2019 12.48, Alex Shi wrote:
> Now we repeatly assign the lruvec->pgdat in memcg. Will remove the
> assignment in lruvec getting function after very points are protected.
>
> Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: cgroups@vger.kernel.org
> Cc: linux-mm@kvack.org
> Cc: linux-kernel@vger.kernel.org
> ---
> mm/memcontrol.c | 12 +++++-------
> 1 file changed, 5 insertions(+), 7 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index e8a1b0d95ba8..19fd911e8098 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2550,12 +2550,12 @@ 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);
> + struct lruvec *lruvec = mem_cgroup_page_lruvec(page, pgdat);
>

What protects lruvec from freeing at this point?
After reading resolving lruvec page could be moved and cgroup deleted.

In this old patches I've used RCU for that: https://lkml.org/lkml/2012/2/20/276
Pointer to lruvec should be resolved under disabled irq.
Not sure this works these days.

> - spin_lock_irq(&pgdat->lruvec.lru_lock);
> + spin_lock_irq(&lruvec->lru_lock);
> + sync_lruvec_pgdat(lruvec, pgdat);
> if (PageLRU(page)) {
> - struct lruvec *lruvec;
>
> - lruvec = mem_cgroup_page_lruvec(page, pgdat);
> ClearPageLRU(page);
> del_page_from_lru_list(page, lruvec, page_lru(page));
> *isolated = 1;
> @@ -2566,16 +2566,14 @@ static void lock_page_lru(struct page *page, int *isolated)
> static void unlock_page_lru(struct page *page, int isolated)
> {
> pg_data_t *pgdat = page_pgdat(page);
> + struct lruvec *lruvec = mem_cgroup_page_lruvec(page, pgdat);
>
> if (isolated) {
> - struct lruvec *lruvec;
> -
> - lruvec = mem_cgroup_page_lruvec(page, pgdat);
> VM_BUG_ON_PAGE(PageLRU(page), page);
> SetPageLRU(page);
> add_page_to_lru_list(page, lruvec, page_lru(page));
> }
> - spin_unlock_irq(&pgdat->lruvec.lru_lock);
> + spin_unlock_irq(&lruvec->lru_lock);
> }
>
> static void commit_charge(struct page *page, struct mem_cgroup *memcg,
>

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