Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756269Ab3JGUWM (ORCPT ); Mon, 7 Oct 2013 16:22:12 -0400 Received: from e23smtp07.au.ibm.com ([202.81.31.140]:34785 "EHLO e23smtp07.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755828Ab3JGUWD (ORCPT ); Mon, 7 Oct 2013 16:22:03 -0400 From: Robert C Jennings To: linux-kernel@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Alexander Viro , Rik van Riel , Andrea Arcangeli , Dave Hansen , Robert C Jennings , Matt Helsley , Anthony Liguori , Michael Roth , Lei Li , Leonardo Garcia , Vlastimil Babka Subject: [PATCH 2/2] vmsplice: Add limited zero copy to vmsplice Date: Mon, 7 Oct 2013 15:21:33 -0500 Message-Id: <1381177293-27125-3-git-send-email-rcj@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.2 In-Reply-To: <1381177293-27125-1-git-send-email-rcj@linux.vnet.ibm.com> References: <1381177293-27125-1-git-send-email-rcj@linux.vnet.ibm.com> X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13100720-0260-0000-0000-000003BDE381 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3484 Lines: 112 From: Matt Helsley It is sometimes useful to move anonymous pages over a pipe rather than save/swap them. Check the SPLICE_F_GIFT and SPLICE_F_MOVE flags to see if userspace would like to move such pages. This differs from plain SPLICE_F_GIFT in that the memory written to the pipe will no longer have the same contents as the original -- it effectively faults in new, empty anonymous pages. On the read side the page written to the pipe will be copied unless SPLICE_F_MOVE is used. Otherwise copying will be performed and the page will be reclaimed. Note that so long as there is a mapping to the page copies will be done instead because rmap will have upped the map count for each anonymous mapping; this can happen do to fork(), for example. This is necessary because moving the page will usually change the anonymous page's nonlinear index and that can only be done if it's unmapped. Signed-off-by: Matt Helsley Signed-off-by: Robert C Jennings --- fs/splice.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 63 insertions(+) diff --git a/fs/splice.c b/fs/splice.c index a62d61e..9d2ed128 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -32,6 +32,10 @@ #include #include #include +#include +#include +#include +#include #include "internal.h" /* @@ -1562,6 +1566,65 @@ static int pipe_to_user(struct pipe_inode_info *pipe, struct pipe_buffer *buf, char *src; int ret; + if (!buf->offset && (buf->len == PAGE_SIZE) && + (buf->flags & PIPE_BUF_FLAG_GIFT) && (sd->flags & SPLICE_F_MOVE)) { + struct page *page = buf->page; + struct mm_struct *mm; + struct vm_area_struct *vma; + spinlock_t *ptl; + pte_t *ptep, pte; + unsigned long useraddr; + + if (!PageAnon(page)) + goto copy; + if (PageCompound(page)) + goto copy; + if (PageHuge(page) || PageTransHuge(page)) + goto copy; + if (page_mapped(page)) + goto copy; + useraddr = (unsigned long)sd->u.userptr; + mm = current->mm; + + ret = -EAGAIN; + down_read(&mm->mmap_sem); + vma = find_vma_intersection(mm, useraddr, useraddr + PAGE_SIZE); + if (IS_ERR_OR_NULL(vma)) + goto up_copy; + if (!vma->anon_vma) { + ret = anon_vma_prepare(vma); + if (ret) + goto up_copy; + } + zap_page_range(vma, useraddr, PAGE_SIZE, NULL); + ret = lock_page_killable(page); + if (ret) + goto up_copy; + ptep = get_locked_pte(mm, useraddr, &ptl); + if (!ptep) + goto unlock_up_copy; + pte = *ptep; + if (pte_present(pte)) + goto unlock_up_copy; + get_page(page); + page_add_anon_rmap(page, vma, useraddr); + pte = mk_pte(page, vma->vm_page_prot); + set_pte_at(mm, useraddr, ptep, pte); + update_mmu_cache(vma, useraddr, ptep); + pte_unmap_unlock(ptep, ptl); + ret = 0; +unlock_up_copy: + unlock_page(page); +up_copy: + up_read(&mm->mmap_sem); + if (!ret) { + ret = sd->len; + goto out; + } + /* else ret < 0 and we should fallback to copying */ + VM_BUG_ON(ret > 0); + } +copy: /* * See if we can use the atomic maps, by prefaulting in the * pages and doing an atomic copy -- 1.8.1.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/