From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f199.google.com (mail-wr0-f199.google.com [209.85.128.199]) by kanga.kvack.org (Postfix) with ESMTP id AC8696B0006 for ; Fri, 16 Mar 2018 09:02:27 -0400 (EDT) Received: by mail-wr0-f199.google.com with SMTP id w10so2491042wrg.15 for ; Fri, 16 Mar 2018 06:02:27 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id c7sor3503951edi.56.2018.03.16.06.02.26 for (Google Transport Security); Fri, 16 Mar 2018 06:02:26 -0700 (PDT) Date: Fri, 16 Mar 2018 16:02:00 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCH] mm/shmem: Do not wait for lock_page() in shmem_unused_huge_shrink() Message-ID: <20180316130200.rbke66zjyoc6zwzl@node.shutemov.name> References: <20180316105908.62516-1-kirill.shutemov@linux.intel.com> <20180316121303.GI23100@dhcp22.suse.cz> <20180316122508.fv4edpx34hdqybwx@node.shutemov.name> <20180316125827.GC11461@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180316125827.GC11461@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: "Kirill A. Shutemov" , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Eric Wheeler , Tetsuo Handa On Fri, Mar 16, 2018 at 01:58:27PM +0100, Michal Hocko wrote: > On Fri 16-03-18 15:25:08, Kirill A. Shutemov wrote: > > On Fri, Mar 16, 2018 at 01:13:03PM +0100, Michal Hocko wrote: > > > On Fri 16-03-18 13:59:08, Kirill A. Shutemov wrote: > > > [..] > > > > @@ -498,31 +498,42 @@ static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo, > > > > continue; > > > > } > > > > > > > > - page = find_lock_page(inode->i_mapping, > > > > + page = find_get_page(inode->i_mapping, > > > > (inode->i_size & HPAGE_PMD_MASK) >> PAGE_SHIFT); > > > > if (!page) > > > > goto drop; > > > > > > > > + /* No huge page at the end of the file: nothing to split */ > > > > if (!PageTransHuge(page)) { > > > > - unlock_page(page); > > > > put_page(page); > > > > goto drop; > > > > } > > > > > > > > + /* > > > > + * Leave the inode on the list if we failed to lock > > > > + * the page at this time. > > > > + * > > > > + * Waiting for the lock may lead to deadlock in the > > > > + * reclaim path. > > > > + */ > > > > + if (!trylock_page(page)) { > > > > + put_page(page); > > > > + goto leave; > > > > + } > > > > > > Can somebody split the huge page after the PageTransHuge check and > > > before we lock it? > > > > Nope. Pin on the page is enough to prevent split. > > Good, I thought so but wasn't really 100% sure. Thanks for the > clarification and feel free to add > Acked-by: Michal Hocko Thanks. > Maybe you should stick > Reported-by: Eric Wheeler > and point to http://lkml.kernel.org/r/alpine.LRH.2.11.1801242349220.30642@mail.ewheeler.net > because that smells like a bug that this patch would be fixing. Good point. Andrew, do you want me repost with tags integrated? -- Kirill A. Shutemov