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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 3CC84C47257 for ; Fri, 1 May 2020 17:00:39 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id C4E72206B8 for ; Fri, 1 May 2020 17:00:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C4E72206B8 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 70BB18E0005; Fri, 1 May 2020 13:00:38 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 6954D8E0001; Fri, 1 May 2020 13:00:38 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 55CD38E0005; Fri, 1 May 2020 13:00:38 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0170.hostedemail.com [216.40.44.170]) by kanga.kvack.org (Postfix) with ESMTP id 3A7098E0001 for ; Fri, 1 May 2020 13:00:38 -0400 (EDT) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id E68925851 for ; Fri, 1 May 2020 17:00:37 +0000 (UTC) X-FDA: 76768764114.21.drug86_3f749ae87c83f X-HE-Tag: drug86_3f749ae87c83f X-Filterd-Recvd-Size: 5037 Received: from out30-131.freemail.mail.aliyun.com (out30-131.freemail.mail.aliyun.com [115.124.30.131]) by imf03.hostedemail.com (Postfix) with ESMTP for ; Fri, 1 May 2020 17:00:35 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R151e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01358;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0TxBvIHa_1588352428; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0TxBvIHa_1588352428) by smtp.aliyun-inc.com(127.0.0.1); Sat, 02 May 2020 01:00:31 +0800 Subject: Re: [v2 linux-next PATCH 2/2] mm: khugepaged: don't have to put being freed page back to lru To: "Kirill A. Shutemov" Cc: kirill.shutemov@linux.intel.com, hughd@google.com, aarcange@redhat.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1588279279-61908-1-git-send-email-yang.shi@linux.alibaba.com> <1588279279-61908-2-git-send-email-yang.shi@linux.alibaba.com> <20200501070424.a5uugk7am2yzzx4v@box> From: Yang Shi Message-ID: Date: Fri, 1 May 2020 10:00:24 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20200501070424.a5uugk7am2yzzx4v@box> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US 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 5/1/20 12:04 AM, Kirill A. Shutemov wrote: > On Fri, May 01, 2020 at 04:41:19AM +0800, Yang Shi wrote: >> When khugepaged successfully isolated and copied data from old page to >> collapsed THP, the old page is about to be freed if its last mapcount >> is gone. So putting the page back to lru sounds not that productive in >> this case since the page might be isolated by vmscan but it can't be >> reclaimed by vmscan since it can't be unmapped by try_to_unmap() at all. >> >> Actually if khugepaged is the last user of this page so it can be freed >> directly. So, clearing active and unevictable flags, unlocking and >> dropping refcount from isolate instead of calling putback_lru_page(). > Any reason putback_lru_page() cannot do it internally? I mean if it is > page_count() == 1, free the page. Because it seems putback_lru_page() is just called when the page is *not* about to be freed, for example compaction is aborted, migration is failed on some pages, etc. I checked a couple of places, i.e. compaction, migration, vmscan. All these places free the page (i.e. old page is migrated to new page successfully) via put_page() without putting back to lru. So, it sounds free page in putback_lru_page() may never happen. We could add this, but it sounds khugepaged would be the only path that may free page in putback_lru_page(). So, it sounds less confusing to follow other users IMHO. >> Cc: Kirill A. Shutemov >> Cc: Hugh Dickins >> Cc: Andrea Arcangeli >> Signed-off-by: Yang Shi >> --- >> v2: Check mapcount and skip putback lru if the last mapcount is gone >> >> mm/khugepaged.c | 20 ++++++++++++++------ >> 1 file changed, 14 insertions(+), 6 deletions(-) >> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index 0c8d30b..1fdd677 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -559,10 +559,18 @@ void __khugepaged_exit(struct mm_struct *mm) >> static void release_pte_page(struct page *page) >> { >> mod_node_page_state(page_pgdat(page), >> - NR_ISOLATED_ANON + page_is_file_lru(page), >> - -compound_nr(page)); >> - unlock_page(page); >> - putback_lru_page(page); >> + NR_ISOLATED_ANON + page_is_file_lru(page), -compound_nr(page)); >> + >> + if (total_mapcount(page)) { >> + unlock_page(page); >> + putback_lru_page(page); >> + } else { >> + ClearPageActive(page); >> + ClearPageUnevictable(page); >> + unlock_page(page); >> + /* Drop refcount from isolate */ >> + put_page(page); >> + } >> } >> >> static void release_pte_pages(pte_t *pte, pte_t *_pte, >> @@ -771,8 +779,6 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page, >> } else { >> src_page = pte_page(pteval); >> copy_user_highpage(page, src_page, address, vma); >> - if (!PageCompound(src_page)) >> - release_pte_page(src_page); >> /* >> * ptl mostly unnecessary, but preempt has to >> * be disabled to update the per-cpu stats >> @@ -786,6 +792,8 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page, >> pte_clear(vma->vm_mm, address, _pte); >> page_remove_rmap(src_page, false); >> spin_unlock(ptl); >> + if (!PageCompound(src_page)) >> + release_pte_page(src_page); >> free_page_and_swap_cache(src_page); >> } >> } >> -- >> 1.8.3.1 >> >>