From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 05C94C33C9E for ; Fri, 17 Jan 2020 22:57:22 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id B825621D56 for ; Fri, 17 Jan 2020 22:57:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B825621D56 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 4F19C6B04FD; Fri, 17 Jan 2020 17:57:21 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 4A1546B04FE; Fri, 17 Jan 2020 17:57:21 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3B76E6B04FF; Fri, 17 Jan 2020 17:57:21 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0229.hostedemail.com [216.40.44.229]) by kanga.kvack.org (Postfix) with ESMTP id 2746D6B04FD for ; Fri, 17 Jan 2020 17:57:21 -0500 (EST) Received: from smtpin27.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with SMTP id DF530180AD817 for ; Fri, 17 Jan 2020 22:57:20 +0000 (UTC) X-FDA: 76388639040.27.cent02_7a40cbe4df81d X-HE-Tag: cent02_7a40cbe4df81d X-Filterd-Recvd-Size: 9686 Received: from mga02.intel.com (mga02.intel.com [134.134.136.20]) by imf08.hostedemail.com (Postfix) with ESMTP for ; Fri, 17 Jan 2020 22:57:19 +0000 (UTC) X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 17 Jan 2020 14:57:18 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,331,1574150400"; d="scan'208";a="306381551" Received: from black.fi.intel.com ([10.237.72.28]) by orsmga001.jf.intel.com with ESMTP; 17 Jan 2020 14:57:14 -0800 Received: by black.fi.intel.com (Postfix, from userid 1000) id 9A28C8D; Sat, 18 Jan 2020 00:57:13 +0200 (EET) Date: Sat, 18 Jan 2020 01:57:13 +0300 From: "Kirill A. Shutemov" To: Wei Yang Cc: Yang Shi , "Kirill A. Shutemov" , David Rientjes , Michal Hocko , Kirill Tkhai , hannes@cmpxchg.org, vdavydov.dev@gmail.com, akpm@linux-foundation.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, alexander.duyck@gmail.com, stable@vger.kernel.org Subject: Re: [Patch v3] mm: thp: grab the lock before manipulation defer list Message-ID: <20200117225713.6acrtyuymklccglv@black.fi.intel.com> References:<20200116013100.7679-1-richardw.yang@linux.intel.com> <0bb34c4a-97c7-0b3c-cf43-8af6cf9c4396@virtuozzo.com> <20200117091002.GM19428@dhcp22.suse.cz> <20200117153839.pcnfomzuaha3dafh@box> <4d117021-da90-6069-1991-4df2249567f8@linux.alibaba.com> <20200117221859.GA29229@richard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To:<20200117221859.GA29229@richard> User-Agent: NeoMutt/20170714-126-deb55f (1.8.3) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Jan 17, 2020 at 10:18:59PM +0000, Wei Yang wrote: > On Fri, Jan 17, 2020 at 11:17:38AM -0800, Yang Shi wrote: > > > > > >On 1/17/20 7:38 AM, Kirill A. Shutemov wrote: > >> On Fri, Jan 17, 2020 at 01:31:50AM -0800, David Rientjes wrote: > >> > On Fri, 17 Jan 2020, Michal Hocko wrote: > >> > > >> > > On Thu 16-01-20 14:01:59, David Rientjes wrote: > >> > > > On Thu, 16 Jan 2020, Kirill Tkhai wrote: > >> > > > > >> > > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > >> > > > > > index c5b5f74cfd4d..6450bbe394e2 100644 > >> > > > > > --- a/mm/memcontrol.c > >> > > > > > +++ b/mm/memcontrol.c > >> > > > > > @@ -5360,10 +5360,12 @@ static int mem_cgroup_move_account(struct page *page, > >> > > > > > } > >> > > > > > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > >> > > > > > - if (compound && !list_empty(page_deferred_list(page))) { > >> > > > > > + if (compound) { > >> > > > > > spin_lock(&from->deferred_split_queue.split_queue_lock); > >> > > > > > - list_del_init(page_deferred_list(page)); > >> > > > > > - from->deferred_split_queue.split_queue_len--; > >> > > > > > + if (!list_empty(page_deferred_list(page))) { > >> > > > > > + list_del_init(page_deferred_list(page)); > >> > > > > > + from->deferred_split_queue.split_queue_len--; > >> > > > > > + } > >> > > > > > spin_unlock(&from->deferred_split_queue.split_queue_lock); > >> > > > > > } > >> > > > > > #endif > >> > > > > > @@ -5377,11 +5379,13 @@ static int mem_cgroup_move_account(struct page *page, > >> > > > > > page->mem_cgroup = to; > >> > > > > > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > >> > > > > > - if (compound && list_empty(page_deferred_list(page))) { > >> > > > > > + if (compound) { > >> > > > > > 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++; > >> > > > > > + if (list_empty(page_deferred_list(page))) { > >> > > > > > + 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 > >> > > > > The patch looks OK for me. But there is another question. I forget, why we unconditionally > >> > > > > add a page with empty deferred list to deferred_split_queue. Shouldn't we also check that > >> > > > > it was initially in the list? Something like: > >> > > > > > >> > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > >> > > > > index d4394ae4e5be..0be0136adaa6 100644 > >> > > > > --- a/mm/memcontrol.c > >> > > > > +++ b/mm/memcontrol.c > >> > > > > @@ -5289,6 +5289,7 @@ static int mem_cgroup_move_account(struct page *page, > >> > > > > struct pglist_data *pgdat; > >> > > > > unsigned long flags; > >> > > > > unsigned int nr_pages = compound ? hpage_nr_pages(page) : 1; > >> > > > > + bool split = false; > >> > > > > int ret; > >> > > > > bool anon; > >> > > > > @@ -5346,6 +5347,7 @@ static int mem_cgroup_move_account(struct page *page, > >> > > > > if (!list_empty(page_deferred_list(page))) { > >> > > > > list_del_init(page_deferred_list(page)); > >> > > > > from->deferred_split_queue.split_queue_len--; > >> > > > > + split = true; > >> > > > > } > >> > > > > spin_unlock(&from->deferred_split_queue.split_queue_lock); > >> > > > > } > >> > > > > @@ -5360,7 +5362,7 @@ static int mem_cgroup_move_account(struct page *page, > >> > > > > page->mem_cgroup = to; > >> > > > > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > >> > > > > - if (compound) { > >> > > > > + if (compound && split) { > >> > > > > spin_lock(&to->deferred_split_queue.split_queue_lock); > >> > > > > if (list_empty(page_deferred_list(page))) { > >> > > > > list_add_tail(page_deferred_list(page), > >> > > > > > >> > > > I think that's a good point, especially considering that the current code > >> > > > appears to unconditionally place any compound page on the deferred split > >> > > > queue of the destination memcg. The correct list that it should appear > >> > > > on, I believe, depends on whether the pmd has been split for the process > >> > > > being moved: note the MC_TARGET_PAGE caveat in > >> > > > mem_cgroup_move_charge_pte_range() that does not move the charge for > >> > > > compound pages with split pmds. So when mem_cgroup_move_account() is > >> > > > called with compound == true, we're moving the charge of the entire > >> > > > compound page: why would it appear on that memcg's deferred split queue? > >> > > I believe Kirill asked how do we know that the page should be actually > >> > > added to the deferred list just from the list_empty check. In other > >> > > words what if the page hasn't been split at all? > >> > > > >> > Right, and I don't think that it necessarily is and the second > >> > conditional in Wei's patch will always succeed unless we have raced. That > >> > patch is for a lock concern but I think Kirill's question has uncovered > >> > something more interesting. > >> > > >> > Kirill S would definitely be best to answer Kirill T's question, but from > >> > my understanding when mem_cgroup_move_account() is called with > >> > compound == true that we always have an intact pmd (we never migrate > >> > partial page charges for pages on the deferred split queue with the > >> > current charge migration implementation) and thus the underlying page is > >> > not eligible to be split and shouldn't be on the deferred split queue. > >> > > >> > In other words, a page being on the deferred split queue for a memcg > >> > should only happen when it is charged to that memcg. (This wasn't the > >> > case when we only had per-node split queues.) I think that's currently > >> > broken in mem_cgroup_move_account() before Wei's patch. > >> Right. It's broken indeed. > > > >Hmm... Yes, definitely. I wasn't realized this at the first place. > > > >> > >> We are dealing with anon page here. And it cannot be on deferred list as > >> long as it's mapped with PMD. We cannot get compound == true && > >> !list_empty() on the (first) enter to the function. Any PMD-mapped page > >> will be put onto deferred by the function. This is wrong. > >> > >> The fix is not obvious. > >> > >> This comment got in mem_cgroup_move_charge_pte_range() my attention: > >> > >> /* > >> * We can have a part of the split pmd here. Moving it > >> * can be done but it would be too convoluted so simply > >> * ignore such a partial THP and keep it in original > >> * memcg. There should be somebody mapping the head. > >> */ > >> > >> That's exactly the case we care about: PTE-mapped THP that has to be split > >> under load. We don't move charge of them between memcgs and therefore we > >> should not move the page to different memcg. > >> > >> I guess this will do the trick :P > > > >It seems correct to me. In addition, memcg move charge just move PMD mapped > >THP, the THP should be never on the deferred split queue of "from" if it is > >PMD mapped, so actually we don't have to move it to the deferred split queue > >of "to". > > > > Well, I got the point. > > Since Kirill S found the correct solution, should I prepare v3 or Kirill will > send it? Go ahead. With my Suggested-by. -- Kirill A. Shutemov