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[114.179.232.161]) by mx.google.com with ESMTPS id 62si9621120ota.263.2019.06.12.00.25.36 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 12 Jun 2019 00:25:36 -0700 (PDT) Received-SPF: pass (google.com: domain of n-horiguchi@ah.jp.nec.com designates 114.179.232.161 as permitted sender) client-ip=114.179.232.161; Authentication-Results: mx.google.com; spf=pass (google.com: domain of n-horiguchi@ah.jp.nec.com designates 114.179.232.161 as permitted sender) smtp.mailfrom=n-horiguchi@ah.jp.nec.com Received: from mailgate02.nec.co.jp ([114.179.233.122]) by tyo161.gate.nec.co.jp (8.15.1/8.15.1) with ESMTPS id x5C7PHkF003196 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Wed, 12 Jun 2019 16:25:17 +0900 Received: from mailsv02.nec.co.jp (mailgate-v.nec.co.jp [10.204.236.94]) by mailgate02.nec.co.jp (8.15.1/8.15.1) with ESMTP id x5C7PHli001893; Wed, 12 Jun 2019 16:25:17 +0900 Received: from mail03.kamome.nec.co.jp (mail03.kamome.nec.co.jp [10.25.43.7]) by mailsv02.nec.co.jp (8.15.1/8.15.1) with ESMTP id x5C7N0Oo021490; Wed, 12 Jun 2019 16:25:17 +0900 Received: from bpxc99gp.gisp.nec.co.jp ([10.38.151.150] [10.38.151.150]) by mail03.kamome.nec.co.jp with ESMTP id BT-MMP-1234399; Wed, 12 Jun 2019 16:09:34 +0900 Received: from BPXM23GP.gisp.nec.co.jp ([10.38.151.215]) by BPXC22GP.gisp.nec.co.jp ([10.38.151.150]) with mapi id 14.03.0319.002; Wed, 12 Jun 2019 16:09:34 +0900 From: Naoya Horiguchi To: Anshuman Khandual CC: "linux-mm@kvack.org" , Andrew Morton , Michal Hocko , Mike Kravetz , "xishi.qiuxishi@alibaba-inc.com" , "Chen, Jerry T" , "Zhuo, Qiuxu" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v2 2/2] mm: hugetlb: soft-offline: dissolve_free_huge_page() return zero on !PageHuge Thread-Topic: [PATCH v2 2/2] mm: hugetlb: soft-offline: dissolve_free_huge_page() return zero on !PageHuge Thread-Index: AQHVH2UOI3n3iV7mFEufJF8BQjmdkqaVoIYAgAFlaYA= Date: Wed, 12 Jun 2019 07:09:32 +0000 Message-ID: <20190612070939.GA25452@hori.linux.bs1.fc.nec.co.jp> References: <1560154686-18497-1-git-send-email-n-horiguchi@ah.jp.nec.com> <1560154686-18497-3-git-send-email-n-horiguchi@ah.jp.nec.com> <4a1ea5f4-d35d-f3a6-920c-c35520234aa3@arm.com> In-Reply-To: <4a1ea5f4-d35d-f3a6-920c-c35520234aa3@arm.com> Accept-Language: en-US, ja-JP Content-Language: ja-JP X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.34.125.150] Content-Type: text/plain; charset="iso-2022-jp" Content-ID: <1DD66F49A3CF854696A42373F9F2F2E2@gisp.nec.co.jp> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-TM-AS-MML: disable 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 Tue, Jun 11, 2019 at 03:20:26PM +0530, Anshuman Khandual wrote: >=20 > On 06/10/2019 01:48 PM, Naoya Horiguchi wrote: > > madvise(MADV_SOFT_OFFLINE) often returns -EBUSY when calling soft offli= ne > > for hugepages with overcommitting enabled. That was caused by the subop= timal > > code in current soft-offline code. See the following part: > >=20 > > ret =3D migrate_pages(&pagelist, new_page, NULL, MPOL_MF_MOVE_ALL, > > MIGRATE_SYNC, MR_MEMORY_FAILURE); > > if (ret) { > > ... > > } else { > > /* > > * We set PG_hwpoison only when the migration source hugepa= ge > > * was successfully dissolved, because otherwise hwpoisoned > > * hugepage remains on free hugepage list, then userspace w= ill > > * find it as SIGBUS by allocation failure. That's not expe= cted > > * in soft-offlining. > > */ > > ret =3D dissolve_free_huge_page(page); > > if (!ret) { > > if (set_hwpoison_free_buddy_page(page)) > > num_poisoned_pages_inc(); > > } > > } > > return ret; > >=20 > > Here dissolve_free_huge_page() returns -EBUSY if the migration source p= age > > was freed into buddy in migrate_pages(), but even in that case we actua= lly >=20 > Over committed source pages will be released into buddy and the normal on= es > will not be ? dissolve_free_huge_page() returns -EBUSY because PageHuge() > return negative on already released pages ?=20 The answers for both questions here are yes. > How dissolve_free_huge_page() > will behave differently with over committed pages. I might be missing som= e > recent developments here. This dissolve_free_huge_page() should see a (free or reused) 4kB page when overcommitting, and should see a (free or reused) huge page for non overcommitting case. >=20 > > has a chance that set_hwpoison_free_buddy_page() succeeds. So that mean= s > > current code gives up offlining too early now. >=20 > Hmm. It gives up early as the return value from dissolve_free_huge_page(E= BUSY) > gets back as the return code for soft_offline_huge_page() without attempt= ing > set_hwpoison_free_buddy_page() which still has a chance to succeed for fr= eed > normal buddy pages. Exactly. >=20 > >=20 > > dissolve_free_huge_page() checks that a given hugepage is suitable for > > dissolving, where we should return success for !PageHuge() case because > > the given hugepage is considered as already dissolved. >=20 > Right. It should return 0 (as a success) for freed normal buddy pages. Sh= ould > not it then check explicitly for PageBuddy() as well ? in new semantics, dissolve_free_huge_page() returns: 0: successfully dissolved free hugepages or the page is already dissolved EBUSY: failed to dissolved free hugepages or the hugepage is in-use. so for any types of non hugepages, the return value is 0. Thanks, - Naoya=20 > >=20 > > This change also affects other callers of dissolve_free_huge_page(), > > which are cleaned up together. > >=20 > > Reported-by: Chen, Jerry T > > Tested-by: Chen, Jerry T > > Signed-off-by: Naoya Horiguchi > > Fixes: 6bc9b56433b76 ("mm: fix race on soft-offlining") > > Cc: # v4.19+ > > --- > > mm/hugetlb.c | 15 +++++++++------ > > mm/memory-failure.c | 5 +---- > > 2 files changed, 10 insertions(+), 10 deletions(-) > >=20 > > diff --git v5.2-rc3/mm/hugetlb.c v5.2-rc3_patched/mm/hugetlb.c > > index ac843d3..048d071 100644 > > --- v5.2-rc3/mm/hugetlb.c > > +++ v5.2-rc3_patched/mm/hugetlb.c > > @@ -1519,7 +1519,12 @@ int dissolve_free_huge_page(struct page *page) > > int rc =3D -EBUSY; > > =20 > > spin_lock(&hugetlb_lock); > > - if (PageHuge(page) && !page_count(page)) { > > + if (!PageHuge(page)) { > > + rc =3D 0; > > + goto out; > > + } >=20 > With this early bail out it maintains the functionality when called from > soft_offline_free_page() for normal pages. For huge page, it continues > on the previous path. >=20 > > + > > + if (!page_count(page)) { > > struct page *head =3D compound_head(page); > > struct hstate *h =3D page_hstate(head); > > int nid =3D page_to_nid(head); > > @@ -1564,11 +1569,9 @@ int dissolve_free_huge_pages(unsigned long start= _pfn, unsigned long end_pfn) > > =20 > > for (pfn =3D start_pfn; pfn < end_pfn; pfn +=3D 1 << minimum_order) { > > page =3D pfn_to_page(pfn); > > - if (PageHuge(page) && !page_count(page)) { >=20 > Right. These checks are now redundant. > =