From patchwork Fri Sep 1 08:20:26 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vlastimil Babka X-Patchwork-Id: 13372243 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3E051CA0FEC for ; Fri, 1 Sep 2023 08:20:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244010AbjIAIUg (ORCPT ); Fri, 1 Sep 2023 04:20:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57850 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241886AbjIAIUf (ORCPT ); Fri, 1 Sep 2023 04:20:35 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 69B3610DE; Fri, 1 Sep 2023 01:20:32 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id B16B32185C; Fri, 1 Sep 2023 08:20:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1693556430; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=0WI96qvBSKjcD8skIYDzJyfhIXrX2VNlBg1bDAXSO7w=; b=r4AvfguvEQvHBhS4L8lDsEaveieeJTkNCYi5f+9IRURkHs9QHXGXU55bgZKYP/UIN96eLm Su7gVEZFmwF5EXNaNlCErp7Hgj8GQqdQewKT6RBq+dcvYVgxoLUZe9WovHMiX8iQwt+NsA NGR32KTwfyM1j9J07mti1C+WlqZc3DM= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1693556430; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=0WI96qvBSKjcD8skIYDzJyfhIXrX2VNlBg1bDAXSO7w=; b=LDBeIJn7DjHmpeWPe/JUiDen1A1u3hmJEXiXvjRyh5pbOBnd20g14NvrGZHMhmcFppSIaI jb3axaR9hQtT2aCA== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 27C7D1358B; Fri, 1 Sep 2023 08:20:30 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id M/8FCc6e8WSYGwAAMHmgww (envelope-from ); Fri, 01 Sep 2023 08:20:30 +0000 From: Vlastimil Babka To: seanjc@google.com Cc: ackerleytng@google.com, akpm@linux-foundation.org, anup@brainfault.org, aou@eecs.berkeley.edu, chao.p.peng@linux.intel.com, chenhuacai@kernel.org, david@redhat.com, isaku.yamahata@gmail.com, jarkko@kernel.org, jmorris@namei.org, kirill.shutemov@linux.intel.com, kvm-riscv@lists.infradead.org, kvm@vger.kernel.org, kvmarm@lists.linux.dev, liam.merwick@oracle.com, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linux-security-module@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, mail@maciej.szmigiero.name, maz@kernel.org, michael.roth@amd.com, mpe@ellerman.id.au, oliver.upton@linux.dev, palmer@dabbelt.com, paul.walmsley@sifive.com, paul@paul-moore.com, pbonzini@redhat.com, qperret@google.com, serge@hallyn.com, tabba@google.com, vannapurve@google.com, vbabka@suse.cz, wei.w.wang@intel.com, willy@infradead.org, yu.c.zhang@linux.intel.com Subject: [PATCH gmem FIXUP] mm, compaction: make testing mapping_unmovable() safe Date: Fri, 1 Sep 2023 10:20:26 +0200 Message-ID: <20230901082025.20548-2-vbabka@suse.cz> X-Mailer: git-send-email 2.41.0 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org As Kirill pointed out, mapping can be removed under us due to truncation. Test it under folio lock as already done for the async compaction / dirty folio case. To prevent locking every folio with mapping to do the test, do it only for unevictable folios, as we can expect the unmovable mapping folios are also unevictable - it is the case for guest memfd folios. Also incorporate comment update suggested by Matthew. Fixes: 3424873596ce ("mm: Add AS_UNMOVABLE to mark mapping as completely unmovable") Signed-off-by: Vlastimil Babka --- Feel free to squash into 3424873596ce. mm/compaction.c | 49 ++++++++++++++++++++++++++++++++----------------- 1 file changed, 32 insertions(+), 17 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index a3d2b132df52..e0e439b105b5 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -862,6 +862,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, /* Time to isolate some pages for migration */ for (; low_pfn < end_pfn; low_pfn++) { + bool is_dirty, is_unevictable; if (skip_on_failure && low_pfn >= next_skip_pfn) { /* @@ -1047,10 +1048,6 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, if (!mapping && (folio_ref_count(folio) - 1) > folio_mapcount(folio)) goto isolate_fail_put; - /* The mapping truly isn't movable. */ - if (mapping && mapping_unmovable(mapping)) - goto isolate_fail_put; - /* * Only allow to migrate anonymous pages in GFP_NOFS context * because those do not depend on fs locks. @@ -1062,8 +1059,10 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, if (!folio_test_lru(folio)) goto isolate_fail_put; + is_unevictable = folio_test_unevictable(folio); + /* Compaction might skip unevictable pages but CMA takes them */ - if (!(mode & ISOLATE_UNEVICTABLE) && folio_test_unevictable(folio)) + if (!(mode & ISOLATE_UNEVICTABLE) && is_unevictable) goto isolate_fail_put; /* @@ -1075,26 +1074,42 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, if ((mode & ISOLATE_ASYNC_MIGRATE) && folio_test_writeback(folio)) goto isolate_fail_put; - if ((mode & ISOLATE_ASYNC_MIGRATE) && folio_test_dirty(folio)) { - bool migrate_dirty; + is_dirty = folio_test_dirty(folio); + + if (((mode & ISOLATE_ASYNC_MIGRATE) && is_dirty) + || (mapping && is_unevictable)) { + bool migrate_dirty = true; + bool is_unmovable; /* - * Only pages without mappings or that have a - * ->migrate_folio callback are possible to migrate - * without blocking. However, we can be racing with - * truncation so it's necessary to lock the page - * to stabilise the mapping as truncation holds - * the page lock until after the page is removed - * from the page cache. + * Only folios without mappings or that have + * a ->migrate_folio callback are possible to migrate + * without blocking. + * + * Folios from unmovable mappings are not migratable. + * + * However, we can be racing with truncation, which can + * free the mapping that we need to check. Truncation + * holds the folio lock until after the folio is removed + * from the page so holding it ourselves is sufficient. + * + * To avoid this folio locking to inspect every folio + * with mapping for being unmovable, we assume every + * such folio is also unevictable, which is a cheaper + * test. If our assumption goes wrong, it's not a bug, + * just potentially wasted cycles. */ if (!folio_trylock(folio)) goto isolate_fail_put; mapping = folio_mapping(folio); - migrate_dirty = !mapping || - mapping->a_ops->migrate_folio; + if ((mode & ISOLATE_ASYNC_MIGRATE) && is_dirty) { + migrate_dirty = !mapping || + mapping->a_ops->migrate_folio; + } + is_unmovable = mapping && mapping_unmovable(mapping); folio_unlock(folio); - if (!migrate_dirty) + if (!migrate_dirty || is_unmovable) goto isolate_fail_put; }