From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f173.google.com (mail-wi0-f173.google.com [209.85.212.173]) by kanga.kvack.org (Postfix) with ESMTP id C4EFC6B0082 for ; Sun, 29 Mar 2015 13:42:41 -0400 (EDT) Received: by wibgn9 with SMTP id gn9so96084657wib.1 for ; Sun, 29 Mar 2015 10:42:41 -0700 (PDT) Received: from jenni1.inet.fi (mta-out1.inet.fi. [62.71.2.195]) by mx.google.com with ESMTP id u2si13812615wju.72.2015.03.29.10.42.39 for ; Sun, 29 Mar 2015 10:42:40 -0700 (PDT) Date: Sun, 29 Mar 2015 20:42:23 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCHv4 12/24] thp: PMD splitting without splitting compound page Message-ID: <20150329174223.GA976@node.dhcp.inet.fi> References: <1425486792-93161-1-git-send-email-kirill.shutemov@linux.intel.com> <1425486792-93161-13-git-send-email-kirill.shutemov@linux.intel.com> <87ego7n6ha.fsf@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87ego7n6ha.fsf@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Aneesh Kumar K.V" Cc: "Kirill A. Shutemov" , Andrew Morton , Andrea Arcangeli , Dave Hansen , Hugh Dickins , Mel Gorman , Rik van Riel , Vlastimil Babka , Christoph Lameter , Naoya Horiguchi , Steve Capper , Johannes Weiner , Michal Hocko , Jerome Marchand , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Sun, Mar 29, 2015 at 09:25:29PM +0530, Aneesh Kumar K.V wrote: > "Kirill A. Shutemov" writes: > > > Current split_huge_page() combines two operations: splitting PMDs into > > tables of PTEs and splitting underlying compound page. This patch > > changes split_huge_pmd() implementation to split the given PMD without > > splitting other PMDs this page mapped with or underlying compound page. > > > > In order to do this we have to get rid of tail page refcounting, which > > uses _mapcount of tail pages. Tail page refcounting is needed to be able > > to split THP page at any point: we always know which of tail pages is > > pinned (i.e. by get_user_pages()) and can distribute page count > > correctly. > > > > We can avoid this by allowing split_huge_page() to fail if the compound > > page is pinned. This patch removes all infrastructure for tail page > > refcounting and make split_huge_page() to always return -EBUSY. All > > split_huge_page() users already know how to handle its fail. Proper > > implementation will be added later. > > > > Without tail page refcounting, implementation of split_huge_pmd() is > > pretty straight-forward. > > > > Memory cgroup is not yet ready for new refcouting. Let's disable it on > > Kconfig level. > > > > Signed-off-by: Kirill A. Shutemov > ..... > ..... > > > static inline int page_mapped(struct page *page) > > { > > - return atomic_read(&(page)->_mapcount) + compound_mapcount(page) >= 0; > > + int i; > > + if (likely(!PageCompound(page))) > > + return atomic_read(&page->_mapcount) >= 0; > > + if (compound_mapcount(page)) > > + return 1; > > + for (i = 0; i < hpage_nr_pages(page); i++) { > > + if (atomic_read(&page[i]._mapcount) >= 0) > > + return 1; > > + } > > do we need to loop with head page here ? ie, We do need to loop if we have only tail pages mapped. Partial unmap case. > > page = compound_page(page); compound_head() ? This function expects to see head page on input. I'll put VM_BUG_ON() there to make sure we don't call it tail pages. > > + return 0; > > } -- Kirill A. Shutemov -- 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