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 C1B74C33C9E for ; Fri, 17 Jan 2020 22:18:54 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 8011B21D56 for ; Fri, 17 Jan 2020 22:18:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8011B21D56 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 13C896B04F7; Fri, 17 Jan 2020 17:18:54 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 0EF896B04F8; Fri, 17 Jan 2020 17:18:54 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EF7546B04F9; Fri, 17 Jan 2020 17:18:53 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0176.hostedemail.com [216.40.44.176]) by kanga.kvack.org (Postfix) with ESMTP id D687E6B04F7 for ; Fri, 17 Jan 2020 17:18:53 -0500 (EST) Received: from smtpin01.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 873E8485F for ; Fri, 17 Jan 2020 22:18:53 +0000 (UTC) X-FDA: 76388542146.01.ring81_4d8745f25bb2f X-HE-Tag: ring81_4d8745f25bb2f X-Filterd-Recvd-Size: 10723 Received: from mga04.intel.com (mga04.intel.com [192.55.52.120]) by imf05.hostedemail.com (Postfix) with ESMTP for ; Fri, 17 Jan 2020 22:18:52 +0000 (UTC) X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by fmsmga104.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 17 Jan 2020 14:18:51 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,331,1574150400"; d="scan'208";a="424631108" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by fmsmga005.fm.intel.com with ESMTP; 17 Jan 2020 14:18:48 -0800 Date: Sat, 18 Jan 2020 06:18:59 +0800 From: Wei Yang To: Yang Shi Cc: "Kirill A. Shutemov" , David Rientjes , Michal Hocko , Kirill Tkhai , Wei Yang , hannes@cmpxchg.org, vdavydov.dev@gmail.com, akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, 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: <20200117221859.GA29229@richard> Reply-To: Wei Yang 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4d117021-da90-6069-1991-4df2249567f8@linux.alibaba.com> User-Agent: Mutt/1.9.4 (2018-02-28) 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 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? >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index c5b5f74cfd4d..e87ee4c10f6e 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -5359,14 +5359,6 @@ 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 >> @@ -5376,16 +5368,6 @@ 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; -- Wei Yang Help you, Help me