Messages in this thread | | | Subject | Re: [Patch v4] mm: thp: remove the defer list related code since this will not happen | From | Yang Shi <> | Date | Fri, 17 Jan 2020 21:30:45 -0800 |
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On 1/17/20 4:57 PM, Yang Shi wrote: > > > On 1/17/20 3:38 PM, Wei Yang wrote: >> If compound is true, this means it is a PMD mapped THP. Which implies >> the page is not linked to any defer list. So the first code chunk will >> not be executed. >> >> Also with this reason, it would not be proper to add this page to a >> defer list. So the second code chunk is not correct. >> >> Based on this, we should remove the defer list related code. >> >> Fixes: 87eaceb3faa5 ("mm: thp: make deferred split shrinker memcg >> aware") >> >> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com> >> Suggested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> >> Cc: <stable@vger.kernel.org> [5.4+] >> >> --- >> v4: >> * finally we identified the related code is not necessary and not >> correct, just remove it >> * thanks to Kirill T first spot some problem > > Thanks for debugging and figuring this out. Acked-by: Yang Shi > <yang.shi@linux.alibaba.com>
BTW, the patch itself is fine, but the subject looks really confusing. It sounds like we would remove all deferred list code. I'd suggest rephrase it to:
mm: thp: don't need care deferred split queue in memcg charge move path
> >> v3: >> * remove all review/ack tag since rewrite the changelog >> * use deferred_split_huge_page as the example of race >> * add cc stable 5.4+ tag as suggested by David Rientjes >> >> v2: >> * move check on compound outside suggested by Alexander >> * an example of the race condition, suggested by Michal >> --- >> mm/memcontrol.c | 18 ------------------ >> 1 file changed, 18 deletions(-) >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index 6c83cf4ed970..27c231bf4565 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -5340,14 +5340,6 @@ static int mem_cgroup_move_account(struct page >> *page, >> __mod_lruvec_state(to_vec, NR_WRITEBACK, nr_pages); >> } >> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE >> - if (compound && !list_empty(page_deferred_list(page))) { >> - spin_lock(&from->deferred_split_queue.split_queue_lock); >> - list_del_init(page_deferred_list(page)); >> - from->deferred_split_queue.split_queue_len--; >> - spin_unlock(&from->deferred_split_queue.split_queue_lock); >> - } >> -#endif >> /* >> * It is safe to change page->mem_cgroup here because the page >> * is referenced, charged, and isolated - we can't race with >> @@ -5357,16 +5349,6 @@ static int mem_cgroup_move_account(struct page >> *page, >> /* caller should have done css_get */ >> page->mem_cgroup = to; >> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE >> - if (compound && list_empty(page_deferred_list(page))) { >> - spin_lock(&to->deferred_split_queue.split_queue_lock); >> - list_add_tail(page_deferred_list(page), >> - &to->deferred_split_queue.split_queue); >> - to->deferred_split_queue.split_queue_len++; >> - spin_unlock(&to->deferred_split_queue.split_queue_lock); >> - } >> -#endif >> - >> spin_unlock_irqrestore(&from->move_lock, flags); >> ret = 0; >
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