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 X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 064A8C43457 for ; Mon, 19 Oct 2020 18:01:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9099622276 for ; Mon, 19 Oct 2020 18:01:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="dW4Xtc/j" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730048AbgJSSB5 (ORCPT ); Mon, 19 Oct 2020 14:01:57 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:57530 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729511AbgJSSB4 (ORCPT ); Mon, 19 Oct 2020 14:01:56 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1603130515; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=3ZRhVayc2gwj9c+mByvsT99OLPdz2/IY1oQ3zLgfgHU=; b=dW4Xtc/j7nIDsuBSGMmrf0k7KPqw8NhDsArqXjxDkAcH22jXuDheDfuXk5+KcNAA0+5JBb JJ9n41pe+N8Dv4pnRJY/SQOZNbsPFt6DI92MJ6Ac3aktkhcnt7V9+CeyHToQQFMeAbVkNL ZRdQfsJYraidvCFsvmLT5WH34MEbAYo= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-219-7HpEU7DdOLGhX7ZiDHCvIA-1; Mon, 19 Oct 2020 14:01:53 -0400 X-MC-Unique: 7HpEU7DdOLGhX7ZiDHCvIA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 07D62108BBE2; Mon, 19 Oct 2020 18:01:52 +0000 (UTC) Received: from bfoster (ovpn-112-249.rdu2.redhat.com [10.10.112.249]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 833F75D9EF; Mon, 19 Oct 2020 18:01:51 +0000 (UTC) Date: Mon, 19 Oct 2020 14:01:44 -0400 From: Brian Foster To: Christoph Hellwig Cc: linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org Subject: Re: [PATCH 2/2] iomap: zero cached pages over unwritten extents on zero range Message-ID: <20201019180144.GC1232435@bfoster> References: <20201012140350.950064-1-bfoster@redhat.com> <20201012140350.950064-3-bfoster@redhat.com> <20201015094901.GC21420@infradead.org> <20201019165519.GB1232435@bfoster> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201019165519.GB1232435@bfoster> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Mon, Oct 19, 2020 at 12:55:19PM -0400, Brian Foster wrote: > On Thu, Oct 15, 2020 at 10:49:01AM +0100, Christoph Hellwig wrote: > > > +iomap_zero_range_skip_uncached(struct inode *inode, loff_t *pos, > > > + loff_t *count, loff_t *written) > > > +{ > > > + unsigned dirty_offset, bytes = 0; > > > + > > > + dirty_offset = page_cache_seek_hole_data(inode, *pos, *count, > > > + SEEK_DATA); > > > + if (dirty_offset == -ENOENT) > > > + bytes = *count; > > > + else if (dirty_offset > *pos) > > > + bytes = dirty_offset - *pos; > > > + > > > + if (bytes) { > > > + *pos += bytes; > > > + *count -= bytes; > > > + *written += bytes; > > > + } > > > > I find the calling conventions weird. why not return bytes and > > keep the increments/decrements of the three variables in the caller? > > > > No particular reason. IIRC I had it both ways and just landed on this. > I'd change it, but as mentioned in the patch 1 thread I don't think this > patch is sufficient (with or without patch 1) anyways because the page > can also have been reclaimed before we get here. > Christoph, What do you think about introducing behavior specific to iomap_truncate_page() to unconditionally write zeroes over unwritten extents? AFAICT that addresses the race and was historical XFS behavior (via block_truncate_page()) before iomap, so is not without precedent. What I'd probably do is bury the caller's did_zero parameter into a new internal struct iomap_zero_data to pass down into iomap_zero_range_actor(), then extend that structure with a 'zero_unwritten' field such that iomap_zero_range_actor() can do this: if (srcmap->type == IOMAP_HOLE || (srcmap->type == IOMAP_UNWRITTEN && !zdata->zero_unwritten)) return count; iomap_truncate_page() would set that flag either via open coding iomap_zero_range() or creating a new internal wrapper. Hm? Brian > Brian >