From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f198.google.com (mail-io0-f198.google.com [209.85.223.198]) by kanga.kvack.org (Postfix) with ESMTP id 041C86B0006 for ; Thu, 1 Feb 2018 11:00:18 -0500 (EST) Received: by mail-io0-f198.google.com with SMTP id r74so18277237iod.15 for ; Thu, 01 Feb 2018 08:00:18 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id z9sor684955ioe.66.2018.02.01.08.00.16 for (Google Transport Security); Thu, 01 Feb 2018 08:00:17 -0800 (PST) Subject: Re: [Lsf-pc] [LSF/MM TOPIC] Killing reliance on struct page->mapping References: <20180130004347.GD4526@redhat.com> <20180131165646.GI29051@ZenIV.linux.org.uk> <20180131174245.GE2912@redhat.com> <20180131175558.GA30522@ZenIV.linux.org.uk> <20180131181356.GG2912@redhat.com> <35c2908e-b6ba-fc29-0a3c-15cb8cf00256@kernel.dk> <20180201155748.GA3085@redhat.com> From: Jens Axboe Message-ID: <0badeb21-c08b-80bf-6631-a18c67696f74@kernel.dk> Date: Thu, 1 Feb 2018 09:00:13 -0700 MIME-Version: 1.0 In-Reply-To: <20180201155748.GA3085@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Jerome Glisse Cc: Al Viro , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, lsf-pc@lists.linux-foundation.org, linux-block@vger.kernel.org On 2/1/18 8:57 AM, Jerome Glisse wrote: > On Thu, Feb 01, 2018 at 08:34:58AM -0700, Jens Axboe wrote: >> On 1/31/18 11:13 AM, Jerome Glisse wrote: >>> That's one solution, another one is to have struct bio_vec store >>> buffer_head pointer and not page pointer, from buffer_head you can >>> find struct page and using buffer_head and struct page pointer you >>> can walk the KSM rmap_item chain to find back the mapping. This >>> would be needed on I/O error for pending writeback of a newly write >>> protected page, so one can argue that the overhead of the chain lookup >>> to find back the mapping against which to report IO error, is an >>> acceptable cost. >> >> Ehm nope. bio_vec is a generic container for pages, requiring >> buffer_heads to be able to do IO would be insanity. > > The extra pointer dereference would be killing performance ? No, I'm saying that requiring a buffer_head to be able to do IO is insanity. That's how things used to be in the pre-2001 days. -- Jens Axboe -- 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