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    SubjectRe: [PATCH v7 02/10] mm/memcg: fold lru_lock in lock_page_lru
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    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.


    Also I don't like these functions:
    - called lock/unlock but actually also isolates
    - used just once
    - pgdat evaluated twice

    > lruvec = mem_cgroup_page_lruvec(page, pgdat);
    > ClearPageLRU(page);
    > del_page_from_lru_list(page, lruvec, page_lru(page));
    > @@ -2588,17 +2587,17 @@ 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);
    >
    > if (isolated) {
    > + pg_data_t *pgdat = page_pgdat(page);
    > 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->lru_lock);
    > }
    > - spin_unlock_irq(&pgdat->lru_lock);
    > }
    >
    > static void commit_charge(struct page *page, struct mem_cgroup *memcg,
    >

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