From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id 48FE38E0001 for ; Mon, 24 Sep 2018 10:30:30 -0400 (EDT) Received: by mail-ed1-f70.google.com with SMTP id g18-v6so9476647edg.14 for ; Mon, 24 Sep 2018 07:30:30 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id a27-v6si8306384edb.300.2018.09.24.07.30.28 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 24 Sep 2018 07:30:29 -0700 (PDT) Date: Mon, 24 Sep 2018 16:30:27 +0200 From: Michal Hocko Subject: Re: [PATCH] mm/migrate: Split only transparent huge pages when allocation fails Message-ID: <20180924143027.GE18685@dhcp22.suse.cz> References: <1537798495-4996-1-git-send-email-anshuman.khandual@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1537798495-4996-1-git-send-email-anshuman.khandual@arm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Anshuman Khandual Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org On Mon 24-09-18 19:44:55, Anshuman Khandual wrote: > When unmap_and_move[_huge_page] function fails due to lack of memory, the > splitting should happen only for transparent huge pages not for HugeTLB > pages. PageTransHuge() returns true for both THP and HugeTLB pages. Hence > the conditonal check should test PagesHuge() flag to make sure that given > pages is not a HugeTLB one. Well spotted! Have you actually seen this happening or this is review driven? I am wondering what would be the real effect of this mismatch? I have tried to follow to code path but I suspect split_huge_page_to_list would fail for hugetlbfs pages. If there is a more serious effect then we should mark the patch for stable as well. > > Fixes: 94723aafb9 ("mm: unclutter THP migration") > Signed-off-by: Anshuman Khandual Acked-by: Michal Hocko > --- > mm/migrate.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index d6a2e89..d2297fe 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1411,7 +1411,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page, > * we encounter them after the rest of the list > * is processed. > */ > - if (PageTransHuge(page)) { > + if (PageTransHuge(page) && !PageHuge(page)) { > lock_page(page); > rc = split_huge_page_to_list(page, from); > unlock_page(page); > -- > 2.7.4 -- Michal Hocko SUSE Labs