From patchwork Fri Nov 17 21:15:04 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Howells X-Patchwork-Id: 13459405 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="gczhr1jR" 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 A55331BF1 for ; Fri, 17 Nov 2023 13:16:33 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1700255793; 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=a+cTmaciv8sFXDtNEzB6xtMwFyjcuJcgPFS5oMA9nmQ=; b=gczhr1jR37ZokyflsGhK2oZcu/aB+pUQou8JLH70txizI9eGyj2bWsXixsyChN+sqw+DA1 IG6ajjUOBF5U/hMCBo33keK/bT0wMmGHidCIoVK6ZaEFurTUEiin+8Aj1/7xsw1MaiXud1 CJBr29aQ3Z748By4DhxHOu+OKqDJGxc= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-691-DnLASpbENSO235t5Db5Vzg-1; Fri, 17 Nov 2023 16:16:30 -0500 X-MC-Unique: DnLASpbENSO235t5Db5Vzg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id BA00582193E; Fri, 17 Nov 2023 21:16:29 +0000 (UTC) Received: from warthog.procyon.org.com (unknown [10.42.28.16]) by smtp.corp.redhat.com (Postfix) with ESMTP id 267A61121306; Fri, 17 Nov 2023 21:16:27 +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-cachefs@redhat.com, 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 Subject: [PATCH v2 12/51] netfs: Add func to calculate pagecount/size-limited span of an iterator Date: Fri, 17 Nov 2023 21:15:04 +0000 Message-ID: <20231117211544.1740466-13-dhowells@redhat.com> In-Reply-To: <20231117211544.1740466-1-dhowells@redhat.com> References: <20231117211544.1740466-1-dhowells@redhat.com> Precedence: bulk X-Mailing-List: ceph-devel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.3 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 both maximum + * size and maximum number of segments. Returns the size of the span in bytes. + */ +static size_t netfs_limit_bvec(const struct iov_iter *iter, size_t start_offset, + size_t max_size, size_t max_segs) +{ + const struct bio_vec *bvecs = iter->bvec; + unsigned int nbv = iter->nr_segs, ix = 0, nsegs = 0; + size_t len, span = 0, n = iter->count; + size_t skip = iter->iov_offset + start_offset; + + if (WARN_ON(!iov_iter_is_bvec(iter)) || + WARN_ON(start_offset > n) || + n == 0) + return 0; + + while (n && ix < nbv && skip) { + len = bvecs[ix].bv_len; + if (skip < len) + break; + skip -= len; + n -= len; + ix++; + } + + while (n && ix < nbv) { + len = min3(n, bvecs[ix].bv_len - skip, max_size); + span += len; + nsegs++; + ix++; + if (span >= max_size || nsegs >= max_segs) + break; + skip = 0; + n -= 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 segments + * can be larger than a page in size, provided they're physically contiguous. + * 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 = 0; + loff_t pos = iter->xarray_start + iter->iov_offset; + pgoff_t index = pos / PAGE_SIZE; + size_t span = 0, n = iter->count; + + XA_STATE(xas, iter->xarray, index); + + if (WARN_ON(!iov_iter_is_xarray(iter)) || + WARN_ON(start_offset > n) || + n == 0) + return 0; + max_size = 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 = folio_size(folio); + offset = offset_in_folio(folio, pos); + len = min(max_size, flen - offset); + span += len; + nsegs++; + if (span >= max_size || nsegs >= 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 0bc90c4035a2..cd673596b411 100644 --- a/include/linux/netfs.h +++ b/include/linux/netfs.h @@ -326,6 +326,8 @@ 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); int netfs_start_io_read(struct inode *inode); void netfs_end_io_read(struct inode *inode);