From 15b447361794271f4d03c04d82276a841fe06328 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Tue, 15 Dec 2020 14:21:31 -0800 Subject: mm/lru: revise the comments of lru_lock MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Since we changed the pgdat->lru_lock to lruvec->lru_lock, it's time to fix the incorrect comments in code. Also fixed some zone->lru_lock comment error from ancient time. etc. I struggled to understand the comment above move_pages_to_lru() (surely it never calls page_referenced()), and eventually realized that most of it had got separated from shrink_active_list(): move that comment back. Link: https://lkml.kernel.org/r/1604566549-62481-20-git-send-email-alex.shi@linux.alibaba.com Signed-off-by: Hugh Dickins Signed-off-by: Alex Shi Acked-by: Johannes Weiner Acked-by: Vlastimil Babka Cc: Tejun Heo Cc: Andrey Ryabinin Cc: Jann Horn Cc: Mel Gorman Cc: Matthew Wilcox Cc: Alexander Duyck Cc: Andrea Arcangeli Cc: "Chen, Rong A" Cc: Daniel Jordan Cc: "Huang, Ying" Cc: Joonsoo Kim Cc: Kirill A. Shutemov Cc: Kirill A. Shutemov Cc: Konstantin Khlebnikov Cc: Michal Hocko Cc: Michal Hocko Cc: Mika Penttilä Cc: Minchan Kim Cc: Shakeel Butt Cc: Thomas Gleixner Cc: Vladimir Davydov Cc: Wei Yang Cc: Yang Shi Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/filemap.c | 4 ++-- mm/rmap.c | 4 ++-- mm/vmscan.c | 41 +++++++++++++++++++++++------------------ 3 files changed, 27 insertions(+), 22 deletions(-) (limited to 'mm') diff --git a/mm/filemap.c b/mm/filemap.c index 39bb88140680..c178022d7893 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -102,8 +102,8 @@ * ->swap_lock (try_to_unmap_one) * ->private_lock (try_to_unmap_one) * ->i_pages lock (try_to_unmap_one) - * ->pgdat->lru_lock (follow_page->mark_page_accessed) - * ->pgdat->lru_lock (check_pte_range->isolate_lru_page) + * ->lruvec->lru_lock (follow_page->mark_page_accessed) + * ->lruvec->lru_lock (check_pte_range->isolate_lru_page) * ->private_lock (page_remove_rmap->set_page_dirty) * ->i_pages lock (page_remove_rmap->set_page_dirty) * bdi.wb->list_lock (page_remove_rmap->set_page_dirty) diff --git a/mm/rmap.c b/mm/rmap.c index ab16c96efdfb..08c56aaf72eb 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -28,12 +28,12 @@ * hugetlb_fault_mutex (hugetlbfs specific page fault mutex) * anon_vma->rwsem * mm->page_table_lock or pte_lock - * pgdat->lru_lock (in mark_page_accessed, isolate_lru_page) * swap_lock (in swap_duplicate, swap_info_get) * mmlist_lock (in mmput, drain_mmlist and others) * mapping->private_lock (in __set_page_dirty_buffers) - * mem_cgroup_{begin,end}_page_stat (memcg->move_lock) + * lock_page_memcg move_lock (in __set_page_dirty_buffers) * i_pages lock (widely used) + * lruvec->lru_lock (in lock_page_lruvec_irq) * inode->i_lock (in set_page_dirty's __mark_inode_dirty) * bdi.wb->list_lock (in set_page_dirty's __mark_inode_dirty) * sb_lock (within inode_lock in fs/fs-writeback.c) diff --git a/mm/vmscan.c b/mm/vmscan.c index 60705ea598ee..257cba79a96d 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1613,14 +1613,16 @@ static __always_inline void update_lru_sizes(struct lruvec *lruvec, } /** - * pgdat->lru_lock is heavily contended. Some of the functions that + * Isolating page from the lruvec to fill in @dst list by nr_to_scan times. + * + * lruvec->lru_lock is heavily contended. Some of the functions that * shrink the lists perform better by taking out a batch of pages * and working on them outside the LRU lock. * * For pagecache intensive workloads, this function is the hottest * spot in the kernel (apart from copy_*_user functions). * - * Appropriate locks must be held before calling this function. + * Lru_lock must be held before calling this function. * * @nr_to_scan: The number of eligible pages to look through on the list. * @lruvec: The LRU vector to pull pages from. @@ -1814,25 +1816,11 @@ static int too_many_isolated(struct pglist_data *pgdat, int file, } /* - * This moves pages from @list to corresponding LRU list. - * - * We move them the other way if the page is referenced by one or more - * processes, from rmap. - * - * If the pages are mostly unmapped, the processing is fast and it is - * appropriate to hold zone_lru_lock across the whole operation. But if - * the pages are mapped, the processing is slow (page_referenced()) so we - * should drop zone_lru_lock around each page. It's impossible to balance - * this, so instead we remove the pages from the LRU while processing them. - * It is safe to rely on PG_active against the non-LRU pages in here because - * nobody will play with that bit on a non-LRU page. - * - * The downside is that we have to touch page->_refcount against each page. - * But we had to alter page->flags anyway. + * move_pages_to_lru() moves pages from private @list to appropriate LRU list. + * On return, @list is reused as a list of pages to be freed by the caller. * * Returns the number of pages moved to the given lruvec. */ - static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec, struct list_head *list) { @@ -2010,6 +1998,23 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec, return nr_reclaimed; } +/* + * shrink_active_list() moves pages from the active LRU to the inactive LRU. + * + * We move them the other way if the page is referenced by one or more + * processes. + * + * If the pages are mostly unmapped, the processing is fast and it is + * appropriate to hold lru_lock across the whole operation. But if + * the pages are mapped, the processing is slow (page_referenced()), so + * we should drop lru_lock around each page. It's impossible to balance + * this, so instead we remove the pages from the LRU while processing them. + * It is safe to rely on PG_active against the non-LRU pages in here because + * nobody will play with that bit on a non-LRU page. + * + * The downside is that we have to touch page->_refcount against each page. + * But we had to alter page->flags anyway. + */ static void shrink_active_list(unsigned long nr_to_scan, struct lruvec *lruvec, struct scan_control *sc, -- cgit v1.2.3-70-g09d2