From patchwork Thu Mar 16 15:25:52 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Howells X-Patchwork-Id: 13177833 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 1459BC76195 for ; Thu, 16 Mar 2023 15:27:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231417AbjCPP1f (ORCPT ); Thu, 16 Mar 2023 11:27:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58368 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231303AbjCPP1W (ORCPT ); Thu, 16 Mar 2023 11:27:22 -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 03EDB67011 for ; Thu, 16 Mar 2023 08:26:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1678980396; 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=hvyVk2Tm5p69fLI8jM9sCOn8INezqsFYzfTdfGnmvK4=; b=JwxTFk+d2LnIJIRxrp2jNx8AQVkomOKQFjaTc8lDWrzxY2S4ty9fBbY0jiK6tUVM2JrgIj GBGMxyPAJ1Wr7qc3wVs48bsTDPZ9Qdt2IMv/IxFUG8GEyYzHY0toDWeerqj1OwIqoZ46Si NPHfAys7gjJ9R1R+I6BrgIs4is3SGaM= Received: from mimecast-mx02.redhat.com (mx3-rdu2.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-523-Km8kakyRNF2yUKxaser2SQ-1; Thu, 16 Mar 2023 11:26:29 -0400 X-MC-Unique: Km8kakyRNF2yUKxaser2SQ-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id ADED738149BC; Thu, 16 Mar 2023 15:26:28 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.33.36.18]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7ACDF492B00; Thu, 16 Mar 2023 15:26:26 +0000 (UTC) From: David Howells To: Matthew Wilcox , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: David Howells , Al Viro , Christoph Hellwig , Jens Axboe , Jeff Layton , Christian Brauner , Linus Torvalds , netdev@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Bernard Metzler , Tom Talpey , linux-rdma@vger.kernel.org Subject: [RFC PATCH 02/28] Add a special allocator for staging netfs protocol to MSG_SPLICE_PAGES Date: Thu, 16 Mar 2023 15:25:52 +0000 Message-Id: <20230316152618.711970-3-dhowells@redhat.com> In-Reply-To: <20230316152618.711970-1-dhowells@redhat.com> References: <20230316152618.711970-1-dhowells@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org X-Patchwork-State: RFC If a network protocol sendmsg() sees MSG_SPLICE_DATA, it expects that the iterator is of ITER_BVEC type and that all the pages can have refs taken on them with get_page() and discarded with put_page(). Bits of network filesystem protocol data, however, are typically contained in slab memory for which the cleanup method is kfree(), not put_page(), so this doesn't work. Provide a simple allocator, zcopy_alloc(), that allocates a page at a time per-cpu and sequentially breaks off pieces and hands them out with a ref as it's asked for them. The caller disposes of the memory it was given by calling put_page(). When a page is all parcelled out, it is abandoned by the allocator and another page is obtained. The page will get cleaned up when the last skbuff fragment is destroyed. A helper function, zcopy_memdup() is provided to call zcopy_alloc() and copy the data it is given into it. [!] I'm not sure this is the best way to do things. A better way might be to make the network protocol look at the page and copy it if it's a slab object rather than taking a ref on it. Signed-off-by: David Howells cc: Bernard Metzler cc: Tom Talpey cc: "David S. Miller" cc: Eric Dumazet cc: Jakub Kicinski cc: Paolo Abeni cc: Jens Axboe cc: Matthew Wilcox cc: linux-rdma@vger.kernel.org cc: netdev@vger.kernel.org --- include/linux/zcopy_alloc.h | 16 +++++ mm/Makefile | 2 +- mm/zcopy_alloc.c | 129 ++++++++++++++++++++++++++++++++++++ 3 files changed, 146 insertions(+), 1 deletion(-) create mode 100644 include/linux/zcopy_alloc.h create mode 100644 mm/zcopy_alloc.c diff --git a/include/linux/zcopy_alloc.h b/include/linux/zcopy_alloc.h new file mode 100644 index 000000000000..8eb205678073 --- /dev/null +++ b/include/linux/zcopy_alloc.h @@ -0,0 +1,16 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* Defs for for zerocopy filler fragment allocator. + * + * Copyright (C) 2023 Red Hat, Inc. All Rights Reserved. + * Written by David Howells (dhowells@redhat.com) + */ + +#ifndef _LINUX_ZCOPY_ALLOC_H +#define _LINUX_ZCOPY_ALLOC_H + +struct bio_vec; + +int zcopy_alloc(size_t size, struct bio_vec *bvec, gfp_t gfp); +int zcopy_memdup(size_t size, const void *p, struct bio_vec *bvec, gfp_t gfp); + +#endif /* _LINUX_ZCOPY_ALLOC_H */ diff --git a/mm/Makefile b/mm/Makefile index 8e105e5b3e29..3848f43751ee 100644 --- a/mm/Makefile +++ b/mm/Makefile @@ -52,7 +52,7 @@ obj-y := filemap.o mempool.o oom_kill.o fadvise.o \ readahead.o swap.o truncate.o vmscan.o shmem.o \ util.o mmzone.o vmstat.o backing-dev.o \ mm_init.o percpu.o slab_common.o \ - compaction.o \ + compaction.o zcopy_alloc.o \ interval_tree.o list_lru.o workingset.o \ debug.o gup.o mmap_lock.o $(mmu-y) diff --git a/mm/zcopy_alloc.c b/mm/zcopy_alloc.c new file mode 100644 index 000000000000..7b219392e829 --- /dev/null +++ b/mm/zcopy_alloc.c @@ -0,0 +1,129 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* Allocator for zerocopy filler fragments + * + * Copyright (C) 2023 Red Hat, Inc. All Rights Reserved. + * Written by David Howells (dhowells@redhat.com) + * + * Provide a facility whereby pieces of bufferage can be allocated for + * insertion into bio_vec arrays intended for zerocopying, allowing protocol + * stuff to be mixed in with data. + * + * Unlike objects allocated from the slab, the lifetime of these pieces of + * buffer are governed purely by the refcount of the page in which they reside. + */ + +#include +#include +#include +#include +#include + +struct zcopy_alloc_info { + struct folio *folio; /* Page currently being allocated from */ + struct folio *spare; /* Spare page */ + unsigned int used; /* Amount of folio used */ + spinlock_t lock; /* Allocation lock (needs bh-disable) */ +}; + +static struct zcopy_alloc_info __percpu *zcopy_alloc_info; + +static int __init zcopy_alloc_init(void) +{ + zcopy_alloc_info = alloc_percpu(struct zcopy_alloc_info); + if (!zcopy_alloc_info) + panic("Unable to set up zcopy_alloc allocator\n"); + return 0; +} +subsys_initcall(zcopy_alloc_init); + +/** + * zcopy_alloc - Allocate some memory for use in zerocopy + * @size: The amount of memory (maximum 1/2 page). + * @bvec: Where to store the details of the memory + * @gfp: Allocation flags under which to make an allocation + * + * Allocate some memory for use with zerocopy where protocol bits have to be + * mixed in with spliced/zerocopied data. Unlike memory allocated from the + * slab, this memory's lifetime is purely dependent on the folio's refcount. + * + * The way it works is that a folio is allocated and pieces are broken off + * sequentially and given to the allocators with a ref until it no longer has + * enough spare space, at which point the allocator's ref is dropped and a new + * folio is allocated. The folio remains in existence until the last ref held + * by, say, a sk_buff is discarded and then the page is returned to the + * allocator. + * + * Returns 0 on success and -ENOMEM on allocation failure. If successful, the + * details of the allocated memory are placed in *%bvec. + * + * The allocated memory should be disposed of with folio_put(). + */ +int zcopy_alloc(size_t size, struct bio_vec *bvec, gfp_t gfp) +{ + struct zcopy_alloc_info *info; + struct folio *folio, *spare = NULL; + size_t full_size = round_up(size, 8); + + if (WARN_ON_ONCE(full_size > PAGE_SIZE / 2)) + return -ENOMEM; /* Allocate pages */ + +try_again: + info = get_cpu_ptr(zcopy_alloc_info); + + folio = info->folio; + if (folio && folio_size(folio) - info->used < full_size) { + folio_put(folio); + folio = info->folio = NULL; + } + if (spare && !info->spare) { + info->spare = spare; + spare = NULL; + } + if (!folio && info->spare) { + folio = info->folio = info->spare; + info->spare = NULL; + info->used = 0; + } + if (folio) { + bvec_set_folio(bvec, folio, size, info->used); + info->used += full_size; + if (info->used < folio_size(folio)) + folio_get(folio); + else + info->folio = NULL; + } + + put_cpu_ptr(zcopy_alloc_info); + if (folio) { + if (spare) + folio_put(spare); + return 0; + } + + spare = folio_alloc(gfp, 0); + if (!spare) + return -ENOMEM; + goto try_again; +} +EXPORT_SYMBOL(zcopy_alloc); + +/** + * zcopy_memdup - Allocate some memory for use in zerocopy and fill it + * @size: The amount of memory to copy (maximum 1/2 page). + * @p: The source data to copy + * @bvec: Where to store the details of the memory + * @gfp: Allocation flags under which to make an allocation + */ +int zcopy_memdup(size_t size, const void *p, struct bio_vec *bvec, gfp_t gfp) +{ + void *q; + + if (zcopy_alloc(size, bvec, gfp) < 0) + return -ENOMEM; + + q = kmap_local_folio(page_folio(bvec->bv_page), bvec->bv_offset); + memcpy(q, p, size); + kunmap_local(q); + return 0; +} +EXPORT_SYMBOL(zcopy_memdup);