From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4352AC7EE2D for ; Sun, 4 Jun 2023 22:11:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232155AbjFDWLd (ORCPT ); Sun, 4 Jun 2023 18:11:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41950 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229670AbjFDWLc (ORCPT ); Sun, 4 Jun 2023 18:11:32 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C853AB7; Sun, 4 Jun 2023 15:11:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=eN655bXSpArXRBWxuMXlH+of+zA9r+Yq7PoaU0EV9C0=; b=cwrrT8FnD2qCajGgiuyjQZD8me qkF08blGIICVTGMK8RysRVaXNEpSlCmovQYafN6b3jFWttv+xaNHT3BHilXBRA9z0/whNJSsNHy+t IagdAHRrm6dzUUEMKaUx5R7380FFbDKl8a0lxeqt88McxsAmz3aom+Uy6Ax0NM8r6xO8+4JPF0GmY ehK9JK7JUWZvivPgL5r5PbRkpIHhSsd93/uKt2BriNCxzvuY8rifFowQnHKgoZggl6f+iqz4/awVl 4BPhNPQavZT9CKNeVsq5LY0g5+Mkiz5W9fZR5g/XBKhlFDtOnk0617nuu+PQ8wQG3G4TlnaFXKLSr URI4fBfw==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1q5vwc-00BOlU-RE; Sun, 04 Jun 2023 22:11:26 +0000 Date: Sun, 4 Jun 2023 23:11:26 +0100 From: Matthew Wilcox To: "Darrick J. Wong" Cc: linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, Wang Yugui , Dave Chinner , Christoph Hellwig Subject: Re: [PATCH v2 7/7] iomap: Copy larger chunks from userspace Message-ID: References: <20230602222445.2284892-1-willy@infradead.org> <20230602222445.2284892-8-willy@infradead.org> <20230604182952.GH72241@frogsfrogsfrogs> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230604182952.GH72241@frogsfrogsfrogs> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Sun, Jun 04, 2023 at 11:29:52AM -0700, Darrick J. Wong wrote: > On Fri, Jun 02, 2023 at 11:24:44PM +0100, Matthew Wilcox (Oracle) wrote: > > - copied = copy_page_from_iter_atomic(page, offset, bytes, i); > > + copied = copy_page_from_iter_atomic(&folio->page, offset, bytes, i); > > I think I've gotten lost in the weeds. Does copy_page_from_iter_atomic > actually know how to deal with a multipage folio? AFAICT it takes a > page, kmaps it, and copies @bytes starting at @offset in the page. If > a caller feeds it a multipage folio, does that all work correctly? Or > will the pagecache split multipage folios as needed to make it work > right? It's a smidgen inefficient, but it does work. First, it calls page_copy_sane() to check that offset & n fit within the compound page (ie this all predates folios). ... Oh. copy_page_from_iter() handles this correctly. copy_page_from_iter_atomic() doesn't. I'll have to fix this first. Looks like Al fixed copy_page_from_iter() in c03f05f183cd and didn't fix copy_page_from_iter_atomic(). > If we create a 64k folio at pos 0 and then want to write a byte at pos > 40k, does __filemap_get_folio break up the 64k folio so that the folio > returned by iomap_get_folio starts at 40k? Or can the iter code handle > jumping ten pages into a 16-page folio and I just can't see it? Well ... it handles it fine unless it's highmem. p is kaddr + offset, so if offset is 40k, it works correctly on !highmem.