From nobody Thu Dec 18 00:46:06 2025 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 825A0CDB47E for ; Fri, 13 Oct 2023 16:07:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233121AbjJMQHK (ORCPT ); Fri, 13 Oct 2023 12:07:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34076 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232922AbjJMQGO (ORCPT ); Fri, 13 Oct 2023 12:06:14 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 61D5C184 for ; Fri, 13 Oct 2023 09:05:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1697213120; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ontDGl26Z2fbsTnGmpaZePgZN/TS57PItn3SJDCoVuk=; b=bCk9YrM1H8v47Vj2ebW/WC3cq2xIKCPxixI5faTAg7LWZxx/PjzIfBzLtmpfmjRgawtGm1 KIREwl4yjLADtkurnzmgPxjQSCP7h8Mx/n1sW0tSHo7/I+sueAHyrmp5EiVvGPBAXrsOHM O+XiKEkpgj64nyTC70j39Gz1IvY0uWg= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-133-rWbD_8zjPn63ZHOu7ytAzw-1; Fri, 13 Oct 2023 12:05:15 -0400 X-MC-Unique: rWbD_8zjPn63ZHOu7ytAzw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 190583823337; Fri, 13 Oct 2023 16:05:14 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.42.28.226]) by smtp.corp.redhat.com (Postfix) with ESMTP id 97A0425C0; Fri, 13 Oct 2023 16:05:11 +0000 (UTC) From: David Howells To: Jeff Layton , Steve French Cc: David Howells , Matthew Wilcox , Marc Dionne , Paulo Alcantara , Shyam Prasad N , Tom Talpey , Dominique Martinet , Ilya Dryomov , Christian Brauner , linux-afs@lists.infradead.org, linux-cifs@vger.kernel.org, linux-nfs@vger.kernel.org, ceph-devel@vger.kernel.org, v9fs@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-cachefs@redhat.com Subject: [RFC PATCH 14/53] netfs: Add func to calculate pagecount/size-limited span of an iterator Date: Fri, 13 Oct 2023 17:03:43 +0100 Message-ID: <20231013160423.2218093-15-dhowells@redhat.com> In-Reply-To: <20231013160423.2218093-1-dhowells@redhat.com> References: <20231013160423.2218093-1-dhowells@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.1 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Add a function to work out how much of an ITER_BVEC or ITER_XARRAY iterator we can use in a pagecount-limited and size-limited span. This will be used, for example, to limit the number of segments in a subrequest to the maximum number of elements that an RDMA transfer can handle. Signed-off-by: David Howells cc: Jeff Layton cc: linux-cachefs@redhat.com cc: linux-fsdevel@vger.kernel.org cc: linux-mm@kvack.org --- fs/netfs/iterator.c | 97 +++++++++++++++++++++++++++++++++++++++++++ include/linux/netfs.h | 2 + 2 files changed, 99 insertions(+) diff --git a/fs/netfs/iterator.c b/fs/netfs/iterator.c index 2ff07ba655a0..b781bbbf1d8d 100644 --- a/fs/netfs/iterator.c +++ b/fs/netfs/iterator.c @@ -101,3 +101,100 @@ ssize_t netfs_extract_user_iter(struct iov_iter *orig= , size_t orig_len, return npages; } EXPORT_SYMBOL_GPL(netfs_extract_user_iter); + +/* + * Select the span of a bvec iterator we're going to use. Limit it by bot= h maximum + * size and maximum number of segments. Returns the size of the span in b= ytes. + */ +static size_t netfs_limit_bvec(const struct iov_iter *iter, size_t start_o= ffset, + size_t max_size, size_t max_segs) +{ + const struct bio_vec *bvecs =3D iter->bvec; + unsigned int nbv =3D iter->nr_segs, ix =3D 0, nsegs =3D 0; + size_t len, span =3D 0, n =3D iter->count; + size_t skip =3D iter->iov_offset + start_offset; + + if (WARN_ON(!iov_iter_is_bvec(iter)) || + WARN_ON(start_offset > n) || + n =3D=3D 0) + return 0; + + while (n && ix < nbv && skip) { + len =3D bvecs[ix].bv_len; + if (skip < len) + break; + skip -=3D len; + n -=3D len; + ix++; + } + + while (n && ix < nbv) { + len =3D min3(n, bvecs[ix].bv_len - skip, max_size); + span +=3D len; + nsegs++; + ix++; + if (span >=3D max_size || nsegs >=3D max_segs) + break; + skip =3D 0; + n -=3D len; + } + + return min(span, max_size); +} + +/* + * Select the span of an xarray iterator we're going to use. Limit it by = both + * maximum size and maximum number of segments. It is assumed that segmen= ts + * can be larger than a page in size, provided they're physically contiguo= us. + * Returns the size of the span in bytes. + */ +static size_t netfs_limit_xarray(const struct iov_iter *iter, size_t start= _offset, + size_t max_size, size_t max_segs) +{ + struct folio *folio; + unsigned int nsegs =3D 0; + loff_t pos =3D iter->xarray_start + iter->iov_offset; + pgoff_t index =3D pos / PAGE_SIZE; + size_t span =3D 0, n =3D iter->count; + + XA_STATE(xas, iter->xarray, index); + + if (WARN_ON(!iov_iter_is_xarray(iter)) || + WARN_ON(start_offset > n) || + n =3D=3D 0) + return 0; + max_size =3D min(max_size, n - start_offset); + + rcu_read_lock(); + xas_for_each(&xas, folio, ULONG_MAX) { + size_t offset, flen, len; + if (xas_retry(&xas, folio)) + continue; + if (WARN_ON(xa_is_value(folio))) + break; + if (WARN_ON(folio_test_hugetlb(folio))) + break; + + flen =3D folio_size(folio); + offset =3D offset_in_folio(folio, pos); + len =3D min(max_size, flen - offset); + span +=3D len; + nsegs++; + if (span >=3D max_size || nsegs >=3D max_segs) + break; + } + + rcu_read_unlock(); + return min(span, max_size); +} + +size_t netfs_limit_iter(const struct iov_iter *iter, size_t start_offset, + size_t max_size, size_t max_segs) +{ + if (iov_iter_is_bvec(iter)) + return netfs_limit_bvec(iter, start_offset, max_size, max_segs); + if (iov_iter_is_xarray(iter)) + return netfs_limit_xarray(iter, start_offset, max_size, max_segs); + BUG(); +} +EXPORT_SYMBOL(netfs_limit_iter); diff --git a/include/linux/netfs.h b/include/linux/netfs.h index a7220e906287..2b5e04ea4db2 100644 --- a/include/linux/netfs.h +++ b/include/linux/netfs.h @@ -328,6 +328,8 @@ void netfs_stats_show(struct seq_file *); ssize_t netfs_extract_user_iter(struct iov_iter *orig, size_t orig_len, struct iov_iter *new, iov_iter_extraction_t extraction_flags); +size_t netfs_limit_iter(const struct iov_iter *iter, size_t start_offset, + size_t max_size, size_t max_segs); =20 int netfs_start_io_read(struct inode *inode); void netfs_end_io_read(struct inode *inode);