From patchwork Thu Feb 15 10:32:02 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ryan Roberts X-Patchwork-Id: 13557928 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9F215C48BEB for ; Thu, 15 Feb 2024 10:34:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=TOeULlo5nKeQDUdp6vg/tE5q1GS821QGyQ4hQchIcdE=; b=3ob0q98aEA9tG0 5LRjAmZggpTo+lLn8pbtEzm/rvwAQy8O7FxwRh6mzHDMpYUa6lD2i9M8AaKWWDJnwrDXkChvaHxFI ArxWIMRbN14tfEwwEYlpCtreMGlFQQyXPGaqq70sWT7WhSOiKpHYoRxoEhrPU8vbvPEnu16pgH089 G57SL5tKGP/JuOn6Dj4U+d7yLcHCEC827hCiLcV2lw0pc/ESnQJCSV4xMyYX93k1rA6/G0Grtxia0 1ppZtNys45F9gzr2px4HogNY2d+uNY/lPA2I5ZptGyf87V2ehlgSLVatqYqamJ4Vsqm1p2bokkboF c3YI9y5XzCQf7V8sLMfw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1raZ3u-0000000FmhG-26V8; Thu, 15 Feb 2024 10:33:50 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1raZ3J-0000000FmGt-0N8j for linux-arm-kernel@lists.infradead.org; Thu, 15 Feb 2024 10:33:17 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 20A7A15A1; Thu, 15 Feb 2024 02:33:52 -0800 (PST) Received: from e125769.cambridge.arm.com (e125769.cambridge.arm.com [10.1.196.26]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 17B8B3F7B4; Thu, 15 Feb 2024 02:33:07 -0800 (PST) From: Ryan Roberts To: Catalin Marinas , Will Deacon , Ard Biesheuvel , Marc Zyngier , James Morse , Andrey Ryabinin , Andrew Morton , Matthew Wilcox , Mark Rutland , David Hildenbrand , Kefeng Wang , John Hubbard , Zi Yan , Barry Song <21cnbao@gmail.com>, Alistair Popple , Yang Shi , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" Cc: Ryan Roberts , linux-arm-kernel@lists.infradead.org, x86@kernel.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v6 15/18] mm: Add pte_batch_hint() to reduce scanning in folio_pte_batch() Date: Thu, 15 Feb 2024 10:32:02 +0000 Message-Id: <20240215103205.2607016-16-ryan.roberts@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20240215103205.2607016-1-ryan.roberts@arm.com> References: <20240215103205.2607016-1-ryan.roberts@arm.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240215_023313_396588_65404F1D X-CRM114-Status: GOOD ( 17.30 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Some architectures (e.g. arm64) can tell from looking at a pte, if some follow-on ptes also map contiguous physical memory with the same pgprot. (for arm64, these are contpte mappings). Take advantage of this knowledge to optimize folio_pte_batch() so that it can skip these ptes when scanning to create a batch. By default, if an arch does not opt-in, folio_pte_batch() returns a compile-time 1, so the changes are optimized out and the behaviour is as before. arm64 will opt-in to providing this hint in the next patch, which will greatly reduce the cost of ptep_get() when scanning a range of contptes. Acked-by: David Hildenbrand Tested-by: John Hubbard Signed-off-by: Ryan Roberts --- include/linux/pgtable.h | 21 +++++++++++++++++++++ mm/memory.c | 19 ++++++++++++------- 2 files changed, 33 insertions(+), 7 deletions(-) diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h index bc005d84f764..a36cf4e124b0 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h @@ -212,6 +212,27 @@ static inline int pmd_dirty(pmd_t pmd) #define arch_flush_lazy_mmu_mode() do {} while (0) #endif +#ifndef pte_batch_hint +/** + * pte_batch_hint - Number of pages that can be added to batch without scanning. + * @ptep: Page table pointer for the entry. + * @pte: Page table entry. + * + * Some architectures know that a set of contiguous ptes all map the same + * contiguous memory with the same permissions. In this case, it can provide a + * hint to aid pte batching without the core code needing to scan every pte. + * + * An architecture implementation may ignore the PTE accessed state. Further, + * the dirty state must apply atomically to all the PTEs described by the hint. + * + * May be overridden by the architecture, else pte_batch_hint is always 1. + */ +static inline unsigned int pte_batch_hint(pte_t *ptep, pte_t pte) +{ + return 1; +} +#endif + #ifndef pte_advance_pfn static inline pte_t pte_advance_pfn(pte_t pte, unsigned long nr) { diff --git a/mm/memory.c b/mm/memory.c index 3b8e56eb08a3..4dd8e35b593a 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -988,16 +988,20 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, { unsigned long folio_end_pfn = folio_pfn(folio) + folio_nr_pages(folio); const pte_t *end_ptep = start_ptep + max_nr; - pte_t expected_pte = __pte_batch_clear_ignored(pte_next_pfn(pte), flags); - pte_t *ptep = start_ptep + 1; + pte_t expected_pte, *ptep; bool writable; + int nr; if (any_writable) *any_writable = false; VM_WARN_ON_FOLIO(!pte_present(pte), folio); - while (ptep != end_ptep) { + nr = pte_batch_hint(start_ptep, pte); + expected_pte = __pte_batch_clear_ignored(pte_advance_pfn(pte, nr), flags); + ptep = start_ptep + nr; + + while (ptep < end_ptep) { pte = ptep_get(ptep); if (any_writable) writable = !!pte_write(pte); @@ -1011,17 +1015,18 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, * corner cases the next PFN might fall into a different * folio. */ - if (pte_pfn(pte) == folio_end_pfn) + if (pte_pfn(pte) >= folio_end_pfn) break; if (any_writable) *any_writable |= writable; - expected_pte = pte_next_pfn(expected_pte); - ptep++; + nr = pte_batch_hint(ptep, pte); + expected_pte = pte_advance_pfn(expected_pte, nr); + ptep += nr; } - return ptep - start_ptep; + return min(ptep - start_ptep, max_nr); } /*