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@linux.alibaba.com
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mika Penttilä <mika.penttila@nextfour.com>
Cc: Alexander Duyck <alexander.duyck@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: "Chen, Rong A" <rong.a.chen@intel.com>
Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Jann Horn <jannh@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index f33a6148e4c25251294e25b42edfaa5bcc0a4c95..e8ccf8979648c7f2fb484059b9cea05c821d5aac 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2367,24 +2367,16 @@ static void lru_add_page_tail(struct page *head, struct page *tail,
        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);
        }
 }