From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-f54.google.com (mail-wg0-f54.google.com [74.125.82.54]) by kanga.kvack.org (Postfix) with ESMTP id DBB4F6B0038 for ; Wed, 4 Mar 2015 07:09:56 -0500 (EST) Received: by wghn12 with SMTP id n12so46289506wgh.1 for ; Wed, 04 Mar 2015 04:09:56 -0800 (PST) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id xx1si1164180wjc.205.2015.03.04.04.09.55 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 04 Mar 2015 04:09:55 -0800 (PST) Message-ID: <54F6F60F.4070705@suse.cz> Date: Wed, 04 Mar 2015 13:09:51 +0100 From: Vlastimil Babka MIME-Version: 1.0 Subject: Re: [PATCHv3 04/24] rmap: add argument to charge compound page References: <1423757918-197669-1-git-send-email-kirill.shutemov@linux.intel.com> <1423757918-197669-5-git-send-email-kirill.shutemov@linux.intel.com> <54EB538B.7040308@suse.cz> <20150304115244.GA16452@node.dhcp.inet.fi> In-Reply-To: <20150304115244.GA16452@node.dhcp.inet.fi> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: "Kirill A. Shutemov" , Andrew Morton , Andrea Arcangeli , Hugh Dickins , Dave Hansen , Mel Gorman , Rik van Riel , Christoph Lameter , Naoya Horiguchi , Steve Capper , "Aneesh Kumar K.V" , Johannes Weiner , Michal Hocko , Jerome Marchand , linux-kernel@vger.kernel.org, linux-mm@kvack.org On 03/04/2015 12:52 PM, Kirill A. Shutemov wrote: > On Mon, Feb 23, 2015 at 05:21:31PM +0100, Vlastimil Babka wrote: >> On 02/12/2015 05:18 PM, Kirill A. Shutemov wrote: >>> @@ -1052,21 +1052,24 @@ void page_add_anon_rmap(struct page *page, >>> * Everybody else should continue to use page_add_anon_rmap above. >>> */ >>> void do_page_add_anon_rmap(struct page *page, >>> - struct vm_area_struct *vma, unsigned long address, int exclusive) >>> + struct vm_area_struct *vma, unsigned long address, int flags) >>> { >>> int first = atomic_inc_and_test(&page->_mapcount); >>> if (first) { >>> + bool compound = flags & RMAP_COMPOUND; >>> + int nr = compound ? hpage_nr_pages(page) : 1; >> >> hpage_nr_pages(page) is: >> >> static inline int hpage_nr_pages(struct page *page) >> { >> if (unlikely(PageTransHuge(page))) >> return HPAGE_PMD_NR; >> return 1; >> } >> >> and later... >> >>> /* >>> * We use the irq-unsafe __{inc|mod}_zone_page_stat because >>> * these counters are not modified in interrupt context, and >>> * pte lock(a spinlock) is held, which implies preemption >>> * disabled. >>> */ >>> - if (PageTransHuge(page)) >>> + if (compound) { >>> + VM_BUG_ON_PAGE(!PageTransHuge(page), page); >> >> this means that we could assume that >> (compound == true) => (PageTransHuge(page) == true) >> >> and simplify above to: >> >> int nr = compound ? HPAGE_PMD_NR : 1; >> >> Right? > > No. HPAGE_PMD_NR is defined based on HPAGE_PMD_SHIFT which is BUILD_BUG() > without CONFIG_TRANSPARENT_HUGEPAGE. We will get compiler error without > the helper. Oh, OK. But that doesn't mean there couldn't be another helper that would work in this case, or even open-coded #ifdefs in these functions. Apparently "compound" has to be always false for !CONFIG_TRANSPARENT_HUGEPAGE, as in that case PageTransHuge is defined as 0 and the VM_BUG_ON would trigger if compound was true. So without such ifdefs or wrappers, you are also adding dead code and pointless tests for !CONFIG_TRANSPARENT_HUGEPAGE? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org