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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 D9A14C28CBF for ; Mon, 27 May 2019 07:55:47 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 9039D2070D for ; Mon, 27 May 2019 07:55:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9039D2070D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 335C26B0270; Mon, 27 May 2019 03:55:47 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2E7116B0271; Mon, 27 May 2019 03:55:47 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1D4296B0272; Mon, 27 May 2019 03:55:47 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from mail-pl1-f200.google.com (mail-pl1-f200.google.com [209.85.214.200]) by kanga.kvack.org (Postfix) with ESMTP id D65F46B0270 for ; Mon, 27 May 2019 03:55:46 -0400 (EDT) Received: by mail-pl1-f200.google.com with SMTP id x14so10748862pln.6 for ; Mon, 27 May 2019 00:55:46 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-original-authentication-results:x-gm-message-state:from:to:cc :subject:references:date:in-reply-to:message-id:user-agent :mime-version:content-transfer-encoding; bh=HEVptXv3vS4UM3D+0CZNFIR8J0y3C1pPEfMQkYUBGEk=; b=MkNPm1wW8xNCGXb2qGz3sQobqk6MfTY/2hgpMAcLoR6m4cjsHapyPzYeVlTPx+Qjlr FZQOKdY3tR/4BpuCjysnopJcrxzZNGj6UHvfcVgo18fLkfv9mP96XbW1PIzMDfO0rvzR 995pgHKoEjW8wQvsffixRVlcLTV/PxK2HTPrt6Tkr1UKENXOLHU5pS/18G3a00jKc1I7 2nB9W4hWhYGkVMqkfc4qRIkLqigMzg4cpk7aGOoG2UkGKTVYde3O87rXZQgkATWQ383b T5yHQxMMe6xGMCbrHm6Cm3Pg2d2GZgQc9MsVrAuGH7VZls1NM/Vas8XDZroi+dZFfh5A H8/w== X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of ying.huang@intel.com designates 192.55.52.151 as permitted sender) smtp.mailfrom=ying.huang@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Gm-Message-State: APjAAAVQ6W7WASUfLD2iJ8jefgfGbuMLTw0rF5lCXs0S+/dBYs1EQ/xX ElKZz5AajrMfzyvmXB6FbPqp+1royI22JKhHF+a1q+DPeDVGE1L0IK/0BRjOpgKgbUcQ8nBWW0t pvAreR/+9bTqQys/ohK6c/VssAqAn/kuNKOdHojXDW/bDHCF6twDsQZFk5cBX17z3dw== X-Received: by 2002:a17:902:e492:: with SMTP id cj18mr66371423plb.341.1558943746519; Mon, 27 May 2019 00:55:46 -0700 (PDT) X-Google-Smtp-Source: APXvYqxDdWREgejykqI1N5lpcqwhDnwu78YI6+HsPUzv0XaRnq+5gcHqgNkLKt9fxwFNJyDr1u3Q X-Received: by 2002:a17:902:e492:: with SMTP id cj18mr66371356plb.341.1558943745721; Mon, 27 May 2019 00:55:45 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1558943745; cv=none; d=google.com; s=arc-20160816; b=XehWdscyN84VLwv7KaiHUfhzl7m6H+7b6EmEFHvyBnWoSFmSo2kItDaZeC0po847hf UGai6Mfz8c6Ac6N9Bs18/0f/s+kdD5amCA9JZWBSVJM2We7xugE9MjDe7FeZh1m+solu BNBKeSXRGm/4RCFTMRaHa1sDjSPvU17lYUsuYTOmk/J1Hggc3j6m57mwJc9KIGWl7HmO +L8g+qxYw6oz8vuYmKh8wfKhS3nKdCUaY4T/jnDgaVSFsUMRIknqedRrKxvzEOaIQ+Ht yXkRrjYXJGILxZqBJgFEjcs7jdZSSg03sew9+SKX/hjchHZN4ziyTgfGQa+P5diLrw1K lv1g== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=content-transfer-encoding:mime-version:user-agent:message-id :in-reply-to:date:references:subject:cc:to:from; bh=HEVptXv3vS4UM3D+0CZNFIR8J0y3C1pPEfMQkYUBGEk=; b=oQzuO4qM/J/ZxcOAQdNBwLsV7ZinCNIR9EJHpTR7o2El1p+hkYbzqKj4iWrb/MCga7 P8nLDP78rYi8fYTsBiWOEty4RuO5apHSv/AzWR8RTuiTv9+96/4crRGaV4goB+8TopR5 LVI6/+bSFAsw9r4l2YkmtM+NoW24wr6ixkUi5U5uTseeS5LZ3p5SD2p+Dn16M3QiPQmq gQWU6cQsF+GFwrhjLjw+xommHm024BSGGiw64mg0NYwBkokViqDTuGBbN2KiizQyTWM4 pP8cQ6394uzrc3vhtI4fgOOjFIr6dkoWF76yKf4SvNeZZmxRJENXbZ+1Uisx52jpTUVG +alg== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of ying.huang@intel.com designates 192.55.52.151 as permitted sender) smtp.mailfrom=ying.huang@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com Received: from mga17.intel.com (mga17.intel.com. [192.55.52.151]) by mx.google.com with ESMTPS id d21si15828574pgv.353.2019.05.27.00.55.45 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 27 May 2019 00:55:45 -0700 (PDT) Received-SPF: pass (google.com: domain of ying.huang@intel.com designates 192.55.52.151 as permitted sender) client-ip=192.55.52.151; Authentication-Results: mx.google.com; spf=pass (google.com: domain of ying.huang@intel.com designates 192.55.52.151 as permitted sender) smtp.mailfrom=ying.huang@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga107.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 27 May 2019 00:55:44 -0700 X-ExtLoop1: 1 Received: from yhuang-dev.sh.intel.com (HELO yhuang-dev) ([10.239.159.29]) by orsmga008.jf.intel.com with ESMTP; 27 May 2019 00:55:42 -0700 From: "Huang\, Ying" To: Yang Shi Cc: , , , , , , , , , , Subject: Re: [v6 PATCH 2/2] mm: vmscan: correct some vmscan counters for THP swapout References: <1558929166-3363-1-git-send-email-yang.shi@linux.alibaba.com> <1558929166-3363-2-git-send-email-yang.shi@linux.alibaba.com> <87ef4k8jgs.fsf@yhuang-dev.intel.com> Date: Mon, 27 May 2019 15:55:41 +0800 In-Reply-To: (Yang Shi's message of "Mon, 27 May 2019 15:40:52 +0800") Message-ID: <87a7f88h6q.fsf@yhuang-dev.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit 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: Yang Shi writes: > On 5/27/19 3:06 PM, Huang, Ying wrote: >> Yang Shi writes: >> >>> Since commit bd4c82c22c36 ("mm, THP, swap: delay splitting THP after >>> swapped out"), THP can be swapped out in a whole. But, nr_reclaimed >>> and some other vm counters still get inc'ed by one even though a whole >>> THP (512 pages) gets swapped out. >>> >>> This doesn't make too much sense to memory reclaim. For example, direct >>> reclaim may just need reclaim SWAP_CLUSTER_MAX pages, reclaiming one THP >>> could fulfill it. But, if nr_reclaimed is not increased correctly, >>> direct reclaim may just waste time to reclaim more pages, >>> SWAP_CLUSTER_MAX * 512 pages in worst case. >>> >>> And, it may cause pgsteal_{kswapd|direct} is greater than >>> pgscan_{kswapd|direct}, like the below: >>> >>> pgsteal_kswapd 122933 >>> pgsteal_direct 26600225 >>> pgscan_kswapd 174153 >>> pgscan_direct 14678312 >>> >>> nr_reclaimed and nr_scanned must be fixed in parallel otherwise it would >>> break some page reclaim logic, e.g. >>> >>> vmpressure: this looks at the scanned/reclaimed ratio so it won't >>> change semantics as long as scanned & reclaimed are fixed in parallel. >>> >>> compaction/reclaim: compaction wants a certain number of physical pages >>> freed up before going back to compacting. >>> >>> kswapd priority raising: kswapd raises priority if we scan fewer pages >>> than the reclaim target (which itself is obviously expressed in order-0 >>> pages). As a result, kswapd can falsely raise its aggressiveness even >>> when it's making great progress. >>> >>> Other than nr_scanned and nr_reclaimed, some other counters, e.g. >>> pgactivate, nr_skipped, nr_ref_keep and nr_unmap_fail need to be fixed >>> too since they are user visible via cgroup, /proc/vmstat or trace >>> points, otherwise they would be underreported. >>> >>> When isolating pages from LRUs, nr_taken has been accounted in base >>> page, but nr_scanned and nr_skipped are still accounted in THP. It >>> doesn't make too much sense too since this may cause trace point >>> underreport the numbers as well. >>> >>> So accounting those counters in base page instead of accounting THP as >>> one page. >>> >>> nr_dirty, nr_unqueued_dirty, nr_congested and nr_writeback are used by >>> file cache, so they are not impacted by THP swap. >>> >>> This change may result in lower steal/scan ratio in some cases since >>> THP may get split during page reclaim, then a part of tail pages get >>> reclaimed instead of the whole 512 pages, but nr_scanned is accounted >>> by 512, particularly for direct reclaim. But, this should be not a >>> significant issue. >>> >>> Cc: "Huang, Ying" >>> Cc: Johannes Weiner >>> Cc: Michal Hocko >>> Cc: Mel Gorman >>> Cc: "Kirill A . Shutemov" >>> Cc: Hugh Dickins >>> Cc: Shakeel Butt >>> Cc: Hillf Danton >>> Signed-off-by: Yang Shi >>> --- >>> v6: Fixed the other double account issue introduced by v5 per Huang Ying >>> v5: Fixed sc->nr_scanned double accounting per Huang Ying >>> Added some comments to address the concern about premature OOM per Hillf Danton >>> v4: Fixed the comments from Johannes and Huang Ying >>> v3: Removed Shakeel's Reviewed-by since the patch has been changed significantly >>> Switched back to use compound_order per Matthew >>> Fixed more counters per Johannes >>> v2: Added Shakeel's Reviewed-by >>> Use hpage_nr_pages instead of compound_order per Huang Ying and William Kucharski >>> >>> mm/vmscan.c | 47 +++++++++++++++++++++++++++++++++++------------ >>> 1 file changed, 35 insertions(+), 12 deletions(-) >>> >>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>> index b65bc50..378edff 100644 >>> --- a/mm/vmscan.c >>> +++ b/mm/vmscan.c >>> @@ -1118,6 +1118,7 @@ static unsigned long shrink_page_list(struct list_head *page_list, >>> int may_enter_fs; >>> enum page_references references = PAGEREF_RECLAIM_CLEAN; >>> bool dirty, writeback; >>> + unsigned int nr_pages; >>> cond_resched(); >>> @@ -1129,7 +1130,10 @@ static unsigned long >>> shrink_page_list(struct list_head *page_list, >>> VM_BUG_ON_PAGE(PageActive(page), page); >>> - sc->nr_scanned++; >>> + nr_pages = 1 << compound_order(page); >>> + >>> + /* Account the number of base pages even though THP */ >>> + sc->nr_scanned += nr_pages; >>> if (unlikely(!page_evictable(page))) >>> goto activate_locked; >>> @@ -1250,7 +1254,7 @@ static unsigned long shrink_page_list(struct list_head *page_list, >>> case PAGEREF_ACTIVATE: >>> goto activate_locked; >>> case PAGEREF_KEEP: >>> - stat->nr_ref_keep++; >>> + stat->nr_ref_keep += nr_pages; >>> goto keep_locked; >>> case PAGEREF_RECLAIM: >>> case PAGEREF_RECLAIM_CLEAN: >>> @@ -1306,6 +1310,15 @@ static unsigned long shrink_page_list(struct list_head *page_list, >>> } >>> /* >>> + * THP may get split above, need minus tail pages and update >>> + * nr_pages to avoid accounting tail pages twice. >>> + */ >>> + if ((nr_pages > 1) && !PageTransHuge(page)) { >>> + sc->nr_scanned -= (nr_pages - 1); >>> + nr_pages = 1; >>> + } >> After checking the code again, it appears there's another hole in the >> code. In the following code snippet. >> >> if (!add_to_swap(page)) { >> if (!PageTransHuge(page)) >> goto activate_locked; >> /* Fallback to swap normal pages */ >> if (split_huge_page_to_list(page, >> page_list)) >> goto activate_locked; >> #ifdef CONFIG_TRANSPARENT_HUGEPAGE >> count_vm_event(THP_SWPOUT_FALLBACK); >> #endif >> if (!add_to_swap(page)) >> goto activate_locked; >> } >> >> >> If the THP is split, but the first or the second add_to_swap() fails, we >> still need to deal with sc->nr_scanned and nr_pages. >> >> How about add a new label before "activate_locked" to deal with that? > > It sounds not correct. If swapout fails it jumps to activate_locked > too, it has to be handled in if (!add_to_swap(page)). The below fix > should be good enough since only THP can reach here: > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 378edff..fff3937 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1294,8 +1294,15 @@ static unsigned long shrink_page_list(struct > list_head *page_list, >  #ifdef CONFIG_TRANSPARENT_HUGEPAGE > count_vm_event(THP_SWPOUT_FALLBACK); >  #endif > -                                       if (!add_to_swap(page)) > +                                       if (!add_to_swap(page)) { > +                                               /* > +                                                * Minus tail pages > and reset > +                                                * nr_pages. > +                                                */ > +                                               sc->nr_scanned -= > (nr_pages - 1); > +                                               nr_pages = 1; >                                                 goto activate_locked; > +                                       } >                                 } I think you need to add similar logic for the first add_to_swap() in the original code snippet. >> if (!add_to_swap(page)) { >> if (!PageTransHuge(page)) To reduce code duplication, I suggest to add another label to deal with it. activate_locked_split: if (nr_pages > 1) { sc->nr_scanned -= nr_pages - 1; nr_pages = 1; } activate_locked: And use "goto active_locked_split" if add_to_swap() failed. Best Regards, Huang, Ying