Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756586Ab3JQOBH (ORCPT ); Thu, 17 Oct 2013 10:01:07 -0400 Received: from e23smtp06.au.ibm.com ([202.81.31.148]:40549 "EHLO e23smtp06.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755478Ab3JQOBE (ORCPT ); Thu, 17 Oct 2013 10:01:04 -0400 Date: Thu, 17 Oct 2013 08:44:18 -0500 From: Robert Jennings To: Vlastimil Babka Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Alexander Viro , Rik van Riel , Andrea Arcangeli , Dave Hansen , Matt Helsley , Anthony Liguori , Michael Roth , Lei Li , Leonardo Garcia Subject: Re: [PATCH 2/2] vmsplice: Add limited zero copy to vmsplice Message-ID: <20131017134418.GA19741@linux.vnet.ibm.com> Mail-Followup-To: Vlastimil Babka , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Alexander Viro , Rik van Riel , Andrea Arcangeli , Dave Hansen , Matt Helsley , Anthony Liguori , Michael Roth , Lei Li , Leonardo Garcia References: <1381177293-27125-1-git-send-email-rcj@linux.vnet.ibm.com> <1381177293-27125-3-git-send-email-rcj@linux.vnet.ibm.com> <525FC89E.6040208@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <525FC89E.6040208@suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13101714-7014-0000-0000-000003C8C224 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4190 Lines: 123 * Vlastimil Babka (vbabka@suse.cz) wrote: > On 10/07/2013 10:21 PM, Robert C Jennings wrote: > > 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. > > You might want to update comments of vmsplice_to_user() and > SYSCALL_DEFINE4(vmsplice) as they both explain how it's done only via > copying. > > Vlastimil > I will update those as well. Thanks. > > 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 > > > -- 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/