From: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx> Subject: mm/thp: narrow lru locking lru_lock and page cache xa_lock have no obvious reason to be taken one way round or the other: until now, lru_lock has been taken before page cache xa_lock, when splitting a THP; but nothing else takes them together. Reverse that ordering: let's narrow the lru locking - but leave local_irq_disable to block interrupts throughout, like before. Hugh Dickins point: split_huge_page_to_list() was already silly, to be using the _irqsave variant: it's just been taking sleeping locks, so would already be broken if entered with interrupts enabled. So we can save passing flags argument down to __split_huge_page(). Why change the lock ordering here? That was hard to decide. One reason: when this series reaches per-memcg lru locking, it relies on the THP's memcg to be stable when taking the lru_lock: that is now done after the THP's refcount has been frozen, which ensures page memcg cannot change. Another reason: previously, lock_page_memcg()'s move_lock was presumed to nest inside lru_lock; but now lru_lock must nest inside (page cache lock inside) move_lock, so it becomes possible to use lock_page_memcg() to stabilize page memcg before taking its lru_lock. That is not the mechanism used in this series, but it is an option we want to keep open. [hughd@xxxxxxxxxx: rewrite commit log] Link: https://lkml.kernel.org/r/1604566549-62481-5-git-send-email-alex.shi@xxxxxxxxxxxxxxxxx Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Acked-by: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Alexander Duyck <alexander.duyck@xxxxxxxxx> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> Cc: "Chen, Rong A" <rong.a.chen@xxxxxxxxx> Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> Cc: "Huang, Ying" <ying.huang@xxxxxxxxx> Cc: Jann Horn <jannh@xxxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Cc: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Mika Penttilä <mika.penttila@xxxxxxxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: Shakeel Butt <shakeelb@xxxxxxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: Wei Yang <richard.weiyang@xxxxxxxxx> Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/huge_memory.c | 25 +++++++++++++------------ 1 file changed, 13 insertions(+), 12 deletions(-) --- a/mm/huge_memory.c~mm-thp-narrow-lru-locking +++ a/mm/huge_memory.c @@ -2446,7 +2446,7 @@ static void __split_huge_page_tail(struc } static void __split_huge_page(struct page *page, struct list_head *list, - pgoff_t end, unsigned long flags) + pgoff_t end) { struct page *head = compound_head(page); pg_data_t *pgdat = page_pgdat(head); @@ -2456,8 +2456,6 @@ static void __split_huge_page(struct pag unsigned int nr = thp_nr_pages(head); int i; - lruvec = mem_cgroup_page_lruvec(head, pgdat); - /* complete memcg works before add pages to LRU */ mem_cgroup_split_huge_fixup(head); @@ -2469,6 +2467,11 @@ static void __split_huge_page(struct pag xa_lock(&swap_cache->i_pages); } + /* prevent PageLRU to go away from under us, and freeze lru stats */ + spin_lock(&pgdat->lru_lock); + + lruvec = mem_cgroup_page_lruvec(head, pgdat); + for (i = nr - 1; i >= 1; i--) { __split_huge_page_tail(head, i, lruvec, list); /* Some pages can be beyond i_size: drop them from page cache */ @@ -2488,6 +2491,8 @@ static void __split_huge_page(struct pag } ClearPageCompound(head); + spin_unlock(&pgdat->lru_lock); + /* Caller disabled irqs, so they are still disabled here */ split_page_owner(head, nr); @@ -2505,8 +2510,7 @@ static void __split_huge_page(struct pag page_ref_add(head, 2); xa_unlock(&head->mapping->i_pages); } - - spin_unlock_irqrestore(&pgdat->lru_lock, flags); + local_irq_enable(); remap_page(head, nr); @@ -2652,12 +2656,10 @@ bool can_split_huge_page(struct page *pa int split_huge_page_to_list(struct page *page, struct list_head *list) { struct page *head = compound_head(page); - struct pglist_data *pgdata = NODE_DATA(page_to_nid(head)); struct deferred_split *ds_queue = get_deferred_split_queue(head); struct anon_vma *anon_vma = NULL; struct address_space *mapping = NULL; int count, mapcount, extra_pins, ret; - unsigned long flags; pgoff_t end; VM_BUG_ON_PAGE(is_huge_zero_page(head), head); @@ -2718,9 +2720,8 @@ int split_huge_page_to_list(struct page unmap_page(head); VM_BUG_ON_PAGE(compound_mapcount(head), head); - /* prevent PageLRU to go away from under us, and freeze lru stats */ - spin_lock_irqsave(&pgdata->lru_lock, flags); - + /* block interrupt reentry in xa_lock and spinlock */ + local_irq_disable(); if (mapping) { XA_STATE(xas, &mapping->i_pages, page_index(head)); @@ -2750,7 +2751,7 @@ int split_huge_page_to_list(struct page __dec_lruvec_page_state(head, NR_FILE_THPS); } - __split_huge_page(page, list, end, flags); + __split_huge_page(page, list, end); ret = 0; } else { if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) { @@ -2764,7 +2765,7 @@ int split_huge_page_to_list(struct page spin_unlock(&ds_queue->split_queue_lock); fail: if (mapping) xa_unlock(&mapping->i_pages); - spin_unlock_irqrestore(&pgdata->lru_lock, flags); + local_irq_enable(); remap_page(head, thp_nr_pages(head)); ret = -EBUSY; } _
