From: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx> Subject: mm/thp: simplify lru_add_page_tail() Simplify lru_add_page_tail(), there are actually only two cases possible: split_huge_page_to_list(), with list supplied and head isolated from lru by its caller; or split_huge_page(), with NULL list and head on lru - because when head is racily isolated from lru, the isolator's reference will stop the split from getting any further than its page_ref_freeze(). So decide between the two cases by "list", but add VM_WARN_ON()s to verify that they match our lru expectations. [Hugh Dickins: rewrite commit log] Link: https://lkml.kernel.org/r/1604566549-62481-4-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: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Mika Penttilä <mika.penttila@xxxxxxxxxxxx> Cc: Alexander Duyck <alexander.duyck@xxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> 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: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> Cc: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> 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 | 20 ++++++-------------- 1 file changed, 6 insertions(+), 14 deletions(-) --- a/mm/huge_memory.c~mm-thp-simplify-lru_add_page_tail +++ a/mm/huge_memory.c @@ -2367,24 +2367,16 @@ static void lru_add_page_tail(struct pag VM_BUG_ON_PAGE(PageLRU(tail), head); lockdep_assert_held(&lruvec_pgdat(lruvec)->lru_lock); - if (!list) - SetPageLRU(tail); - - if (likely(PageLRU(head))) - list_add_tail(&tail->lru, &head->lru); - else if (list) { + if (list) { /* page reclaim is reclaiming a huge page */ + VM_WARN_ON(PageLRU(head)); get_page(tail); list_add_tail(&tail->lru, list); } else { - /* - * Head page has not yet been counted, as an hpage, - * so we must account for each subpage individually. - * - * Put tail on the list at the correct position - * so they all end up in order. - */ - add_page_to_lru_list_tail(tail, lruvec, page_lru(tail)); + /* head is still on lru (and we have it frozen) */ + VM_WARN_ON(!PageLRU(head)); + SetPageLRU(tail); + list_add_tail(&tail->lru, &head->lru); } } _
