From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 96E84C432C3 for ; Fri, 22 Nov 2019 23:53:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6460D20637 for ; Fri, 22 Nov 2019 23:53:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="BSUZSIr0" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727096AbfKVXxr (ORCPT ); Fri, 22 Nov 2019 18:53:47 -0500 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:21573 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726961AbfKVXxq (ORCPT ); Fri, 22 Nov 2019 18:53:46 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1574466825; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=CQZMohj51Rvu4NKQeTHUm4c49yOWaO0z0fTazdBpmzU=; b=BSUZSIr0IFdGQK3hwZnSzw35h84etc4HpJpb+18UhYUz9aSdLZVsokRMzkvVcy93g2Gn0a k7+XzokNwQ+xiwUc1dMcpo9rX0oPg3LOwAMVIB77G3XIuZv0CmmDG0GnQNZyIwJy6nHmDb kpkOkPydqi9a/1KYQ41yMcKRjuZ3gRs= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-34-eUKUTjKfNcuoqx_xi4L-iA-1; Fri, 22 Nov 2019 18:53:44 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8F516802689; Fri, 22 Nov 2019 23:53:42 +0000 (UTC) Received: from max.com (ovpn-204-21.brq.redhat.com [10.40.204.21]) by smtp.corp.redhat.com (Postfix) with ESMTP id CC6135C1B5; Fri, 22 Nov 2019 23:53:38 +0000 (UTC) From: Andreas Gruenbacher To: Linus Torvalds Cc: Steven Whitehouse , Konstantin Khlebnikov , "Kirill A. Shutemov" , linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Alexander Viro , Johannes Weiner , cluster-devel@redhat.com, Ronnie Sahlberg , Steve French , Bob Peterson , Andreas Gruenbacher Subject: [RFC PATCH 2/3] fs: Add FAULT_FLAG_CACHED flag for filemap_fault Date: Sat, 23 Nov 2019 00:53:23 +0100 Message-Id: <20191122235324.17245-3-agruenba@redhat.com> In-Reply-To: <20191122235324.17245-1-agruenba@redhat.com> References: <20191122235324.17245-1-agruenba@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-MC-Unique: eUKUTjKfNcuoqx_xi4L-iA-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Add a FAULT_FLAG_CACHED flag which indicates to filemap_fault that it should only look at the page cache, without triggering filesystem I/O for the actual request or for readahead. When filesystem I/O would be triggered, VM_FAULT_RETRY should be returned instead. This allows the caller to tentatively satisfy a minor page fault out of the page cache, and to retry the operation after taking the necessary steps when that isn't possible. Signed-off-by: Andreas Gruenbacher --- include/linux/mm.h | 4 +++- mm/filemap.c | 43 ++++++++++++++++++++++++++++++------------- 2 files changed, 33 insertions(+), 14 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index a2adf95b3f9c..b3317e4b2607 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -392,6 +392,7 @@ extern pgprot_t protection_map[16]; #define FAULT_FLAG_USER=09=090x40=09/* The fault originated in userspace *= / #define FAULT_FLAG_REMOTE=090x80=09/* faulting for non current tsk/mm */ #define FAULT_FLAG_INSTRUCTION 0x100=09/* The fault was during an instruc= tion fetch */ +#define FAULT_FLAG_CACHED=09=090x200=09/* Only look at the page cache */ =20 #define FAULT_FLAG_TRACE \ =09{ FAULT_FLAG_WRITE,=09=09"WRITE" }, \ @@ -402,7 +403,8 @@ extern pgprot_t protection_map[16]; =09{ FAULT_FLAG_TRIED,=09=09"TRIED" }, \ =09{ FAULT_FLAG_USER,=09=09"USER" }, \ =09{ FAULT_FLAG_REMOTE,=09=09"REMOTE" }, \ -=09{ FAULT_FLAG_INSTRUCTION,=09"INSTRUCTION" } +=09{ FAULT_FLAG_INSTRUCTION,=09"INSTRUCTION" }, \ +=09{ FAULT_FLAG_CACHED,=09=09"CACHED" } =20 /* * vm_fault is filled by the the pagefault handler and passed to the vma's diff --git a/mm/filemap.c b/mm/filemap.c index 024ff0b5fcb6..2297fad3b03a 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2383,7 +2383,7 @@ static int lock_page_maybe_drop_mmap(struct vm_fault = *vmf, struct page *page, =09 * the mmap_sem still held. That's how FAULT_FLAG_RETRY_NOWAIT =09 * is supposed to work. We have way too many special cases.. =09 */ -=09if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT) +=09if (vmf->flags & (FAULT_FLAG_RETRY_NOWAIT | FAULT_FLAG_CACHED)) =09=09return 0; =20 =09*fpin =3D maybe_unlock_mmap_for_io(vmf, *fpin); @@ -2460,26 +2460,28 @@ static struct file *do_sync_mmap_readahead(struct v= m_fault *vmf) * so we want to possibly extend the readahead further. We return the fil= e that * was pinned if we have to drop the mmap_sem in order to do IO. */ -static struct file *do_async_mmap_readahead(struct vm_fault *vmf, -=09=09=09=09=09 struct page *page) +static vm_fault_t do_async_mmap_readahead(struct vm_fault *vmf, +=09=09=09=09=09 struct page *page, +=09=09=09=09=09 struct file **fpin) { =09struct file *file =3D vmf->vma->vm_file; =09struct file_ra_state *ra =3D &file->f_ra; =09struct address_space *mapping =3D file->f_mapping; -=09struct file *fpin =3D NULL; =09pgoff_t offset =3D vmf->pgoff; =20 =09/* If we don't want any read-ahead, don't bother */ =09if (vmf->vma->vm_flags & VM_RAND_READ) -=09=09return fpin; +=09=09return 0; =09if (ra->mmap_miss > 0) =09=09ra->mmap_miss--; =09if (PageReadahead(page)) { -=09=09fpin =3D maybe_unlock_mmap_for_io(vmf, fpin); +=09=09if (vmf->flags & FAULT_FLAG_CACHED) +=09=09=09return VM_FAULT_RETRY; +=09=09*fpin =3D maybe_unlock_mmap_for_io(vmf, *fpin); =09=09page_cache_async_readahead(mapping, ra, file, =09=09=09=09=09 page, offset, ra->ra_pages); =09} -=09return fpin; +=09return 0; } =20 /** @@ -2495,8 +2497,11 @@ static struct file *do_async_mmap_readahead(struct v= m_fault *vmf, * * vma->vm_mm->mmap_sem must be held on entry. * - * If our return value has VM_FAULT_RETRY set, it's because the mmap_sem - * may be dropped before doing I/O or by lock_page_maybe_drop_mmap(). + * This function may drop the mmap_sem before doing I/O or waiting for a p= age + * lock; this is indicated by the VM_FAULT_RETRY flag in our return value. + * Setting FAULT_FLAG_CACHED or FAULT_FLAG_RETRY_NOWAIT in vmf->flags will + * prevent dropping the mmap_sem; in that case, VM_FAULT_RETRY indicates t= hat + * the mmap_sem would have been dropped. * * If our return value does not have VM_FAULT_RETRY set, the mmap_sem * has not been released. @@ -2518,9 +2523,15 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) =09struct page *page; =09vm_fault_t ret =3D 0; =20 -=09max_off =3D DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE); -=09if (unlikely(offset >=3D max_off)) -=09=09return VM_FAULT_SIGBUS; +=09/* +=09 * FAULT_FLAG_CACHED indicates that the inode size is only guaranteed +=09 * to be valid when the page we are looking for is in the page cache. +=09 */ +=09if (!(vmf->flags & FAULT_FLAG_CACHED)) { +=09=09max_off =3D DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE); +=09=09if (unlikely(offset >=3D max_off)) +=09=09=09return VM_FAULT_SIGBUS; +=09} =20 =09/* =09 * Do we have something in the page cache already? @@ -2531,8 +2542,14 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) =09=09 * We found the page, so try async readahead before =09=09 * waiting for the lock. =09=09 */ -=09=09fpin =3D do_async_mmap_readahead(vmf, page); +=09=09ret =3D do_async_mmap_readahead(vmf, page, &fpin); +=09=09if (ret) { +=09=09=09put_page(page); +=09=09=09return ret; +=09=09} =09} else if (!page) { +=09=09if (vmf->flags & FAULT_FLAG_CACHED) +=09=09=09goto out_retry; =09=09/* No page in the page cache at all */ =09=09count_vm_event(PGMAJFAULT); =09=09count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT); --=20 2.20.1