From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from lithops.sigma-star.at ([195.201.40.130]:50498 "EHLO lithops.sigma-star.at" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727540AbeLNLZz (ORCPT ); Fri, 14 Dec 2018 06:25:55 -0500 From: Richard Weinberger To: zhangjun Cc: Alexander Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, "Darrick J . Wong" , hch@lst.de, bfoster@redhat.com, darrick.wong@oracle.com, Dave Chinner , akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, mhocko@suse.com, n-horiguchi@ah.jp.nec.com, mgorman@techsingularity.net, aarcange@redhat.com, willy@infradead.org, linux@dominikbrodowski.net, linux-mm@kvack.org, Gao Xiang Subject: Re: [PATCH] fix page_count in ->iomap_migrate_page() Date: Fri, 14 Dec 2018 12:25:50 +0100 Message-ID: <1618433.IpySj692Hd@blindfold> In-Reply-To: <1544766961-3492-1-git-send-email-openzhangj@gmail.com> References: <1544766961-3492-1-git-send-email-openzhangj@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-fsdevel-owner@vger.kernel.org List-ID: [CC'ing authors of the code plus mm folks] Am Freitag, 14. Dezember 2018, 06:56:01 CET schrieb zhangjun: > IOMAP uses PG_private a little different with buffer_head based > filesystem. > It uses it as marker and when set, the page counter is not incremented, > migrate_page_move_mapping() assumes that PG_private indicates a counter > of +1. > so, we have to pass a extra count of -1 to migrate_page_move_mapping() > if the flag is set. > > Signed-off-by: zhangjun > --- > fs/iomap.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/fs/iomap.c b/fs/iomap.c > index 64ce240..352e58a 100644 > --- a/fs/iomap.c > +++ b/fs/iomap.c > @@ -544,8 +544,17 @@ iomap_migrate_page(struct address_space *mapping, struct page *newpage, > struct page *page, enum migrate_mode mode) > { > int ret; > + int extra_count = 0; > > - ret = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0); > + /* > + * IOMAP uses PG_private as marker and does not raise the page counter. > + * migrate_page_move_mapping() expects a incremented counter if PG_private > + * is set. Therefore pass -1 as extra_count for this case. > + */ > + if (page_has_private(page)) > + extra_count = -1; > + ret = migrate_page_move_mapping(mapping, newpage, page, > + NULL, mode, extra_count); > if (ret != MIGRATEPAGE_SUCCESS) > return ret; This is the third place which needs this workaround. UBIFS, F2FS, and now iomap. I agree with Dave that nobody can assume that PG_private implies an additional page reference. But page migration does that. Including parts of the write back code. Thanks, //richard