From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: allowed pages in the block later, was Re: [Ext2-devel] [PATCH] ext3: avoid sending down non-refcounted pages Date: Mon, 12 Dec 2005 17:25:52 +0000 Message-ID: <20051212172552.GA28652@infradead.org> References: <20051208180900T.fujita.tomonori@lab.ntt.co.jp> <20051208101833.GM14509@schatzie.adilger.int> <20051208134239.GA13376@infradead.org> <20051210164736.6e4eaa3f.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Christoph Hellwig , fujita.tomonori@lab.ntt.co.jp, michaelc@cs.wisc.edu, linux-fsdevel@vger.kernel.org, ext2-devel@lists.sourceforge.net, open-iscsi@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Return-path: Received: from pentafluge.infradead.org ([213.146.154.40]:37513 "EHLO pentafluge.infradead.org") by vger.kernel.org with ESMTP id S932074AbVLLR0A (ORCPT ); Mon, 12 Dec 2005 12:26:00 -0500 To: Andrew Morton Content-Disposition: inline In-Reply-To: <20051210164736.6e4eaa3f.akpm@osdl.org> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Sat, Dec 10, 2005 at 04:47:36PM -0800, Andrew Morton wrote: > Christoph Hellwig wrote: > > > > The problem we're trying to solve here is how do implement network block > > devices (nbd, iscsi) efficiently. The zero copy codepath in the networking > > layer does need to grab additional references to pages. So to use sendpage > > we need a refcountable page. pages used by the slab allocator are not > > normally refcounted so try to do get_page/pub_page on them will break. > > I don't get it. Doing get_page/put_page on a slab-allocated page should do > the right thing? As Arjan mentioned, what would be the right thing? Delaying returning the page to the page pool and disallow reuse until page count reaches zero? All this seems highly impractical.