From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yang Shi Subject: Re: [Patch v4] mm: thp: remove the defer list related code since this will not happen Date: Fri, 17 Jan 2020 16:57:41 -0800 Message-ID: References: <20200117233836.3434-1-richardw.yang@linux.intel.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20200117233836.3434-1-richardw.yang-VuQAYsv1563Yd54FQh9/CA@public.gmane.org> Content-Language: en-US Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Wei Yang , hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org, mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, vdavydov.dev-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, ktkhai-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org, kirill.shutemov-VuQAYsv1563Yd54FQh9/CA@public.gmane.org Cc: cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, alexander.duyck-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, rientjes-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org, stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org 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 > Suggested-by: Kirill A. Shutemov > Cc: [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 > 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;