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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5C14BC433FE for ; Tue, 24 May 2022 19:14:14 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id E6A678D0003; Tue, 24 May 2022 15:14:13 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E190C8D0001; Tue, 24 May 2022 15:14:13 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CDED08D0003; Tue, 24 May 2022 15:14:13 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id B896E8D0001 for ; Tue, 24 May 2022 15:14:13 -0400 (EDT) Received: from smtpin26.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 96381352A5 for ; Tue, 24 May 2022 19:14:13 +0000 (UTC) X-FDA: 79501587186.26.F268DFD Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf17.hostedemail.com (Postfix) with ESMTP id BAABB40025 for ; Tue, 24 May 2022 19:13:43 +0000 (UTC) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 25A55616AB; Tue, 24 May 2022 19:14:12 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AAEC7C34118; Tue, 24 May 2022 19:14:08 +0000 (UTC) Date: Tue, 24 May 2022 20:14:04 +0100 From: Catalin Marinas To: Barry Song <21cnbao@gmail.com> Cc: Andrew Morton , Will Deacon , Linux-MM , LAK , LKML , hanchuanhua , =?utf-8?B?5byg6K+X5piOKFNpbW9uIFpoYW5nKQ==?= , =?utf-8?B?6YOt5YGl?= , Barry Song , "Huang, Ying" , Minchan Kim , Johannes Weiner , Hugh Dickins , Shaohua Li , Rik van Riel , Andrea Arcangeli , Steven Price Subject: Re: [PATCH] arm64: enable THP_SWAP for arm64 Message-ID: References: <20220524071403.128644-1-21cnbao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: BAABB40025 X-Stat-Signature: 341854dk4aetrnr48g636qiamfcskd73 X-Rspam-User: Authentication-Results: imf17.hostedemail.com; dkim=none; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=arm.com (policy=none); spf=pass (imf17.hostedemail.com: domain of cmarinas@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=cmarinas@kernel.org X-HE-Tag: 1653419623-345963 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: On Tue, May 24, 2022 at 10:05:35PM +1200, Barry Song wrote: > On Tue, May 24, 2022 at 8:12 PM Catalin Marinas wrote: > > On Tue, May 24, 2022 at 07:14:03PM +1200, Barry Song wrote: > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > > index d550f5acfaf3..8e3771c56fbf 100644 > > > --- a/arch/arm64/Kconfig > > > +++ b/arch/arm64/Kconfig > > > @@ -98,6 +98,7 @@ config ARM64 > > > select ARCH_WANT_HUGE_PMD_SHARE if ARM64_4K_PAGES || (ARM64_16K_PAGES && !ARM64_VA_BITS_36) > > > select ARCH_WANT_LD_ORPHAN_WARN > > > select ARCH_WANTS_NO_INSTR > > > + select ARCH_WANTS_THP_SWAP if ARM64_4K_PAGES > > > > I'm not opposed to this but I think it would break pages mapped with > > PROT_MTE. We have an assumption in mte_sync_tags() that compound pages > > are not swapped out (or in). With MTE, we store the tags in a slab > > I assume you mean mte_sync_tags() require that THP is not swapped as a whole, > as without THP_SWP, THP is still swapping after being splitted. MTE doesn't stop > THP from swapping through a couple of splitted pages, does it? That's correct, split THP page are swapped out/in just fine. > > object (128-bytes per swapped page) and restore them when pages are > > swapped in. At some point we may teach the core swap code about such > > metadata but in the meantime that was the easiest way. > > If my previous assumption is true, the easiest way to enable THP_SWP > for this moment might be always letting mm fallback to the splitting > way for MTE hardware. For this moment, I care about THP_SWP more as > none of my hardware has MTE. > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index 45c358538f13..d55a2a3e41a9 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -44,6 +44,8 @@ > __flush_tlb_range(vma, addr, end, PUD_SIZE, false, 1) > #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ > > +#define arch_thp_swp_supported !system_supports_mte > + > /* > * Outside of a few very special situations (e.g. hibernation), we always > * use broadcast TLB invalidation instructions, therefore a spurious page > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index 2999190adc22..064b6b03df9e 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -447,4 +447,16 @@ static inline int split_folio_to_list(struct folio *folio, > return split_huge_page_to_list(&folio->page, list); > } > > +/* > + * archs that select ARCH_WANTS_THP_SWAP but don't support THP_SWP due to > + * limitations in the implementation like arm64 MTE can override this to > + * false > + */ > +#ifndef arch_thp_swp_supported > +static inline bool arch_thp_swp_supported(void) > +{ > + return true; > +} > +#endif > + > #endif /* _LINUX_HUGE_MM_H */ > diff --git a/mm/swap_slots.c b/mm/swap_slots.c > index 2b5531840583..dde685836328 100644 > --- a/mm/swap_slots.c > +++ b/mm/swap_slots.c > @@ -309,7 +309,7 @@ swp_entry_t get_swap_page(struct page *page) > entry.val = 0; > > if (PageTransHuge(page)) { > - if (IS_ENABLED(CONFIG_THP_SWAP)) > + if (IS_ENABLED(CONFIG_THP_SWAP) && arch_thp_swp_supported()) > get_swap_pages(1, &entry, HPAGE_PMD_NR); > goto out; I think this should work and with your other proposal it would be limited to MTE pages: #define arch_thp_swp_supported(page) (!test_bit(PG_mte_tagged, &page->flags)) Are THP pages loaded from swap as a whole or are they split? IIRC the splitting still happens but after the swapping out finishes. Even if they are loaded as 4K pages, we still have the mte_save_tags() that only understands small pages currently, so rejecting THP pages is probably best. -- Catalin