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=-6.0 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 15ED8C43460 for ; Mon, 26 Apr 2021 19:15:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DD49061153 for ; Mon, 26 Apr 2021 19:15:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238186AbhDZTQ3 (ORCPT ); Mon, 26 Apr 2021 15:16:29 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:44062 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238172AbhDZTQ1 (ORCPT ); Mon, 26 Apr 2021 15:16:27 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1619464545; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=NjlPen1encdZDkGM0wilUuVPtH5U8CDDV8DYPkgdQBU=; b=i/jhZeHGBpZUzi72TqQ6dwfZSK4OhJIYhawDDlDroEkpOdwv7ORQZQK63e7G6x7qUJXNDT 9o2ocHbbwuu7/qPd3Lg4B/98Bw/Icip1P3Ml1XDzM4lNAqxxfFhkfa4e45J3/vAEnHFAzB Y24bShZNYayCCITzaE+ElgJyI/8Vx70= Received: from mail-qk1-f197.google.com (mail-qk1-f197.google.com [209.85.222.197]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-378-5pARX1ZdPkqZ1plYaPkIng-1; Mon, 26 Apr 2021 15:15:41 -0400 X-MC-Unique: 5pARX1ZdPkqZ1plYaPkIng-1 Received: by mail-qk1-f197.google.com with SMTP id k12-20020a05620a0b8cb02902e028cc62baso21283844qkh.17 for ; Mon, 26 Apr 2021 12:15:41 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:message-id:subject:from:to:cc:date:in-reply-to :references:user-agent:mime-version:content-transfer-encoding; bh=NjlPen1encdZDkGM0wilUuVPtH5U8CDDV8DYPkgdQBU=; b=F3jFtCckxK+o+Jg2FLUvx2mxr7xU2EgnEGI0+9oLpcPkeGToFhraHZj8xEI52YBP1r CyWfx2Kly0W2e6L0Sn8AmsrYLLY5OQctaXxXM/V1NGXpcpzRfPS4zQJ6lYs0hYFDDQFt Fp9dNX0YRDIuLprvFRNfTUCVgcwBDIEe91JTrpEtjPyX+QsZTfcm77d7Xz2dRijrdhh1 EUab084SmqC0bj533sP8Tl++aBDDoKJ21NBNsrQx1tkl2/JzCbiz93qI2nl7aqaMtg23 rbRKLD0fEdzAzAa/T1aNZ+n0p2kpsYl3UClklgtvchDzHZo+M3RvkmhVjE7MZi0ZXz2a PXPA== X-Gm-Message-State: AOAM533ZIYkCvh6Dmoc08TNlbAkjbENFQcYGSHmVmHVPiZKsQiihvB8o QlE2nIxOQvG2WHSK4k8oKrZyYeU1LP/pozME6hEpK4f5mMOQ+sQgTBm3NgZwkx7630hfoZaua+R scKwqA4QqffERxvxkSUz7Zw== X-Received: by 2002:a37:de14:: with SMTP id h20mr18965533qkj.34.1619464540670; Mon, 26 Apr 2021 12:15:40 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwZYRAHl+eWnQtgdg3ck30c64eIGwlxsQ5wJdm+wrQWh9LXuumEJb2NQlXbEra5jinaPsZTlQ== X-Received: by 2002:a37:de14:: with SMTP id h20mr18965510qkj.34.1619464540455; Mon, 26 Apr 2021 12:15:40 -0700 (PDT) Received: from [192.168.1.180] (68-20-15-154.lightspeed.rlghnc.sbcglobal.net. [68.20.15.154]) by smtp.gmail.com with ESMTPSA id c15sm12638215qtg.31.2021.04.26.12.15.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 26 Apr 2021 12:15:40 -0700 (PDT) Message-ID: <8114b7a1151edf52e3a20cf30d2673cd177191bf.camel@redhat.com> Subject: Re: [PATCH v7 01/31] iov_iter: Add ITER_XARRAY From: Jeff Layton To: Al Viro , David Howells Cc: linux-fsdevel@vger.kernel.org, Dave Wysochanski , Marc Dionne , "Matthew Wilcox (Oracle)" , Christoph Hellwig , linux-mm@kvack.org, linux-cachefs@redhat.com, linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org, ceph-devel@vger.kernel.org, v9fs-developer@lists.sourceforge.net, Trond Myklebust , Anna Schumaker , Steve French , Dominique Martinet , linux-kernel@vger.kernel.org Date: Mon, 26 Apr 2021 15:15:39 -0400 In-Reply-To: References: <161918446704.3145707.14418606303992174310.stgit@warthog.procyon.org.uk> <161918448151.3145707.11541538916600921083.stgit@warthog.procyon.org.uk> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.40.0 (3.40.0-1.fc34) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: ceph-devel@vger.kernel.org On Mon, 2021-04-26 at 18:54 +0000, Al Viro wrote: > On Fri, Apr 23, 2021 at 02:28:01PM +0100, David Howells wrote: > > -#define iterate_all_kinds(i, n, v, I, B, K) { \ > > +#define iterate_xarray(i, n, __v, skip, STEP) { \ > > + struct page *head = NULL; \ > > + size_t wanted = n, seg, offset; \ > > + loff_t start = i->xarray_start + skip; \ > > + pgoff_t index = start >> PAGE_SHIFT; \ > > + int j; \ > > + \ > > + XA_STATE(xas, i->xarray, index); \ > > + \ > > + rcu_read_lock(); \ > > + xas_for_each(&xas, head, ULONG_MAX) { \ > > + if (xas_retry(&xas, head)) \ > > + continue; \ > > OK, now I'm really confused; what's to guarantee that restart will not have > you hit the same entry more than once? STEP might be e.g. > > memcpy_to_page(v.bv_page, v.bv_offset, > (from += v.bv_len) - v.bv_len, v.bv_len) > > which is clearly not idempotent - from gets incremented, after all. > What am I missing here? > Not sure I understand the issue you see. If xas_retry returns true, we'll restart, but we won't have called STEP yet for that entry. I don't see how we'd retry there and have an issue with idempotency. > > + if (WARN_ON(xa_is_value(head))) \ > > + break; \ > > + if (WARN_ON(PageHuge(head))) \ > > + break; \ > > + for (j = (head->index < index) ? index - head->index : 0; \ > > + j < thp_nr_pages(head); j++) { \ > > + __v.bv_page = head + j; \ > > + offset = (i->xarray_start + skip) & ~PAGE_MASK; \ > > + seg = PAGE_SIZE - offset; \ > > + __v.bv_offset = offset; \ > > + __v.bv_len = min(n, seg); \ > > + (void)(STEP); \ > > + n -= __v.bv_len; \ > > + skip += __v.bv_len; \ > > + if (n == 0) \ > > + break; \ > > + } \ > > + if (n == 0) \ > > + break; \ > > + } \ > > + rcu_read_unlock(); \ > > + n = wanted - n; \ > > +}