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=-16.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham 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 DC5FCC433E0 for ; Wed, 20 Jan 2021 17:36:30 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 8D29A20705 for ; Wed, 20 Jan 2021 17:36:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8D29A20705 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 12D906B0007; Wed, 20 Jan 2021 12:36:30 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 0DDA46B0008; Wed, 20 Jan 2021 12:36:30 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E9BC66B000A; Wed, 20 Jan 2021 12:36:29 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0222.hostedemail.com [216.40.44.222]) by kanga.kvack.org (Postfix) with ESMTP id CF1226B0007 for ; Wed, 20 Jan 2021 12:36:29 -0500 (EST) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 935F2180AD837 for ; Wed, 20 Jan 2021 17:36:29 +0000 (UTC) X-FDA: 77726857698.12.owl55_0d048082755c Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin12.hostedemail.com (Postfix) with ESMTP id 6A4091800DCB5 for ; Wed, 20 Jan 2021 17:36:29 +0000 (UTC) X-HE-Tag: owl55_0d048082755c X-Filterd-Recvd-Size: 7443 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf48.hostedemail.com (Postfix) with ESMTP for ; Wed, 20 Jan 2021 17:36:28 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 90BA3221FE; Wed, 20 Jan 2021 17:36:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1611164187; bh=IeHJxTh2dLGEMk6hqY4LyIwvV7pcdSMi8pKKcvjOfAM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=iJZgHhD1/ANVgDp81pvXm5mD0T9PCPThgef5eboYUt+npa+A94x20BjQHGiu0dmJH RFd4PARLxLTM3loqluv29GYjc2kOTtvGYrzSKKdC6mUiQJKe3xKI9TVD72369BsSj9 IYuBHTgD2Da0vddlUjEFqyaIerUiWuHvA8d7mRXaB7fwx+T1Vc80Nz5mhWznyOs/yO ygNaKxask7Uek/xI8pL5ZkAbULQkoQh0vnhjiflxc21FB55p4xmmks4wGep9Fr7Dwj Fbr6xkmYPl/0jKgZMVvG6aW5IRu0N38I6ujTTcx88y6krIlWLhfjFLgxRKJeE+u8jW HjO3r97j8wDBw== From: Will Deacon To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, Will Deacon , Catalin Marinas , Jan Kara , Minchan Kim , Andrew Morton , "Kirill A . Shutemov" , Linus Torvalds , Vinayak Menon , Hugh Dickins , Nick Desaulniers , kernel-team@android.com Subject: [PATCH v4 2/8] mm: Allow architectures to request 'old' entries when prefaulting Date: Wed, 20 Jan 2021 17:36:06 +0000 Message-Id: <20210120173612.20913-3-will@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20210120173612.20913-1-will@kernel.org> References: <20210120173612.20913-1-will@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Commit 5c0a85fad949 ("mm: make faultaround produce old ptes") changed the "faultaround" behaviour to initialise prefaulted PTEs as 'old', since this avoids vmscan wrongly assuming that they are hot, despite having never been explicitly accessed by userspace. The change has been shown to benefit numerous arm64 micro-architectures (with hardware access flag) running Android, where both application launch latency and direct reclaim time are significantly reduced (by 10%+ and ~80% respectively). Unfortunately, commit 315d09bf30c2 ("Revert "mm: make faultaround produce old ptes"") reverted the change due to it being identified as the cause of a ~6% regression in unixbench on x86. Experiments on a variety of recent arm64 micro-architectures indicate that unixbench is not affected by the original commit, which appears to yield a 0-1% performance improvement. Since one size does not fit all for the initial state of prefaulted PTEs, introduce arch_wants_old_prefaulted_pte(), which allows an architecture to opt-in to 'old' prefaulted PTEs at runtime based on whatever criteria it may have. Cc: Jan Kara Cc: Minchan Kim Cc: Andrew Morton Cc: Kirill A. Shutemov Cc: Linus Torvalds Reported-by: Vinayak Menon Signed-off-by: Will Deacon --- include/linux/mm.h | 5 ++++- mm/filemap.c | 14 ++++++++++---- mm/memory.c | 20 +++++++++++++++++++- 3 files changed, 33 insertions(+), 6 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 4572a9bc5862..251a2339befb 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -434,6 +434,7 @@ extern pgprot_t protection_map[16]; * @FAULT_FLAG_REMOTE: The fault is not for current task/mm. * @FAULT_FLAG_INSTRUCTION: The fault was during an instruction fetch. * @FAULT_FLAG_INTERRUPTIBLE: The fault can be interrupted by non-fatal = signals. + * @FAULT_FLAG_PREFAULT: Fault was a prefault. * * About @FAULT_FLAG_ALLOW_RETRY and @FAULT_FLAG_TRIED: we can specify * whether we would allow page faults to retry by specifying these two @@ -464,6 +465,7 @@ extern pgprot_t protection_map[16]; #define FAULT_FLAG_REMOTE 0x80 #define FAULT_FLAG_INSTRUCTION 0x100 #define FAULT_FLAG_INTERRUPTIBLE 0x200 +#define FAULT_FLAG_PREFAULT 0x400 =20 /* * The default fault flags that should be used by most of the @@ -501,7 +503,8 @@ static inline bool fault_flag_allow_retry_first(unsig= ned int flags) { FAULT_FLAG_USER, "USER" }, \ { FAULT_FLAG_REMOTE, "REMOTE" }, \ { FAULT_FLAG_INSTRUCTION, "INSTRUCTION" }, \ - { FAULT_FLAG_INTERRUPTIBLE, "INTERRUPTIBLE" } + { FAULT_FLAG_INTERRUPTIBLE, "INTERRUPTIBLE" }, \ + { FAULT_FLAG_PREFAULT, "PREFAULT" } =20 /* * vm_fault is filled by the pagefault handler and passed to the vma's diff --git a/mm/filemap.c b/mm/filemap.c index c1f2dc89b8a7..a6dc97906c8e 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -3019,6 +3019,7 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf, struct address_space *mapping =3D file->f_mapping; pgoff_t last_pgoff =3D start_pgoff; unsigned long address =3D vmf->address; + unsigned long flags =3D vmf->flags; XA_STATE(xas, &mapping->i_pages, start_pgoff); struct page *head, *page; unsigned int mmap_miss =3D READ_ONCE(file->f_ra.mmap_miss); @@ -3051,14 +3052,18 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf= , if (!pte_none(*vmf->pte)) goto unlock; =20 + /* We're about to handle the fault */ + if (vmf->address =3D=3D address) { + vmf->flags &=3D ~FAULT_FLAG_PREFAULT; + ret =3D VM_FAULT_NOPAGE; + } else { + vmf->flags |=3D FAULT_FLAG_PREFAULT; + } + do_set_pte(vmf, page); /* no need to invalidate: a not-present page won't be cached */ update_mmu_cache(vma, vmf->address, vmf->pte); unlock_page(head); - - /* The fault is handled */ - if (vmf->address =3D=3D address) - ret =3D VM_FAULT_NOPAGE; continue; unlock: unlock_page(head); @@ -3067,6 +3072,7 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf, pte_unmap_unlock(vmf->pte, vmf->ptl); out: rcu_read_unlock(); + vmf->flags =3D flags; vmf->address =3D address; WRITE_ONCE(file->f_ra.mmap_miss, mmap_miss); return ret; diff --git a/mm/memory.c b/mm/memory.c index 3e2fc2950ad7..f0e7c589ca9d 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -134,6 +134,18 @@ static inline bool arch_faults_on_old_pte(void) } #endif =20 +#ifndef arch_wants_old_prefaulted_pte +static inline bool arch_wants_old_prefaulted_pte(void) +{ + /* + * Transitioning a PTE from 'old' to 'young' can be expensive on + * some architectures, even if it's performed in hardware. By + * default, "false" means prefaulted entries will be 'young'. + */ + return false; +} +#endif + static int __init disable_randmaps(char *s) { randomize_va_space =3D 0; @@ -3725,11 +3737,17 @@ void do_set_pte(struct vm_fault *vmf, struct page= *page) { struct vm_area_struct *vma =3D vmf->vma; bool write =3D vmf->flags & FAULT_FLAG_WRITE; + bool prefault =3D vmf->flags & FAULT_FLAG_PREFAULT; pte_t entry; =20 flush_icache_page(vma, page); entry =3D mk_pte(page, vma->vm_page_prot); - entry =3D pte_sw_mkyoung(entry); + + if (prefault && arch_wants_old_prefaulted_pte()) + entry =3D pte_mkold(entry); + else + entry =3D pte_sw_mkyoung(entry); + if (write) entry =3D maybe_mkwrite(pte_mkdirty(entry), vma); /* copy-on-write page */ --=20 2.30.0.284.gd98b1dd5eaa7-goog