From mboxrd@z Thu Jan 1 00:00:00 1970 Content-Type: multipart/mixed; boundary="===============5832385852741695275==" MIME-Version: 1.0 From: Hyeonggon Yoo <42.hyeyoo@gmail.com> To: lkp@lists.01.org Subject: Re: [mm/sl[au]b] 3c4cafa313: canonical_address#:#[##] Date: Wed, 14 Sep 2022 15:33:50 +0900 Message-ID: In-Reply-To: List-Id: --===============5832385852741695275== Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable On Fri, Sep 09, 2022 at 11:16:51PM +0200, Vlastimil Babka wrote: > On 9/9/22 16:32, Hyeonggon Yoo wrote: > > On Fri, Sep 09, 2022 at 03:44:19PM +0200, Vlastimil Babka wrote: > >> On 9/9/22 13:05, Hyeonggon Yoo wrote: > >> >> ----8<---- > >> >> From d6f9fbb33b908eb8162cc1f6ce7f7c970d0f285f Mon Sep 17 00:00:00 2= 001 > >> >> From: Vlastimil Babka > >> >> Date: Fri, 9 Sep 2022 12:03:10 +0200 > >> >> Subject: [PATCH 2/3] mm/migrate: make isolate_movable_page() skip s= lab pages > >> >> = > >> >> In the next commit we want to rearrange struct slab fields to allow= a > >> >> larger rcu_head. Afterwards, the page->mapping field will overlap > >> >> with SLUB's "struct list_head slab_list", where the value of prev > >> >> pointer can become LIST_POISON2, which is 0x122 + POISON_POINTER_DE= LTA. > >> >> Unfortunately the bit 1 being set can confuse PageMovable() to be a > >> >> false positive and cause a GPF as reported by lkp [1]. > >> >> = > >> >> To fix this, make isolate_movable_page() skip pages with the PageSl= ab > >> >> flag set. This is a bit tricky as we need to add memory barriers to= SLAB > >> >> and SLUB's page allocation and freeing, and their counterparts to > >> >> isolate_movable_page(). > >> > = > >> > Hello, I just took a quick grasp, > >> > Is this approach okay with folio_test_anon()? > >> = > >> Not if used on a completely random page as compaction scanners can, but > >> relies on those being first tested for PageLRU or coming from a page t= able > >> lookup etc. > >> Not ideal huh. Well I could improve also by switching 'next' and 'slab= s' > >> field and relying on the fact that the value of LIST_POISON2 doesn't i= nclude > >> 0x1, just 0x2. > > = > > What about swapping counters and freelist? > > freelist should be always aligned. = > = > Great suggestion, thanks! > = > Had to deal with SLAB too as there was list_head.prev also aliasing > page->mapping. Wanted to use freelist as well, but turns out it's not > aligned, so had to use s_mem instead. > = > The patch that isolate_movable_page() skip slab pages was thus dropped. T= he > result is in slab.git below and if nothing blows up, will restore it to -= next > = > https://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab.git/log/?h=3D= for-6.1/fit_rcu_head I realized that there is also relevant comment in include/linux/mm_types.h: > 62 * SLUB uses cmpxchg_double() to atomically update its freelist and c= ounters. > 63 * That requires that freelist & counters in struct slab be adjacent = and > 64 * double-word aligned. Because struct slab currently just reinterpre= ts the > 65 * bits of struct page, we align all struct pages to double-word boun= daries, > 66 * and ensure that 'freelist' is aligned within struct slab. > 67 */ Also we may add a comment, something like this? --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -79,6 +79,9 @@ struct page { * WARNING: bit 0 of the first word is used for PageTail(). That * means the other users of this union MUST NOT use the bit to * avoid collision and false-positive PageTail(). + * + * WARNING: lower two bits of third word is used for PAGE_MAPPING_F= LAGS. + * using those bits can lead compaction code to general protection = fault. */ union { struct { /* Page cache and anonymous pages */ = -- = Thanks, Hyeonggon --===============5832385852741695275==-- 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EB09BECAAD3 for ; Wed, 14 Sep 2022 06:34:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229463AbiINGd7 (ORCPT ); Wed, 14 Sep 2022 02:33:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49748 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230016AbiINGd6 (ORCPT ); Wed, 14 Sep 2022 02:33:58 -0400 Received: from mail-pj1-x102e.google.com (mail-pj1-x102e.google.com [IPv6:2607:f8b0:4864:20::102e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ABC75696EC for ; Tue, 13 Sep 2022 23:33:57 -0700 (PDT) Received: by mail-pj1-x102e.google.com with SMTP id d64-20020a17090a6f4600b00202ce056566so8467604pjk.4 for ; Tue, 13 Sep 2022 23:33:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date; bh=Snq77pgWGuBdhSsfi8MS1XPk8bTI55UIIEAHYPZaB1Y=; b=aHOWylDRjar56CZgOKRun2pNmDxLm7upcYLBzSAj46O4d+0lTwTQsK41EDexvCujaB dultCKuPSlmmGBHNThsRee8oRof/okF4pRN4c7I/P9l9GKGhOddsegSuQ6LBGw6o523V gtoY5e6iJpktzqZAM5BReGyBGlkxUChLAu0FwtE5QMRrYaRRqZz5El+SAJdsP3nMHib+ 92Fdk4DZw8JfSYpRRUDG/wav25olLCJEw8Jq4JsIb7TW40etbI2G0MNvVlwAXHiUxMS2 u06FKKVoTYqSX6WpzOY7k2lCZL9MmhxwIXzCNrIJXd9eDXyRekTK8/agon0BKcNBfVYu fw5A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date; bh=Snq77pgWGuBdhSsfi8MS1XPk8bTI55UIIEAHYPZaB1Y=; b=14iiLr0wplet2TYO8zFx3r0tqf6fXrbfGkrB0/ZtEGzyxTupMmpO2IhGjwFRFu/0GU 6ex4VQrH20eCfvWE0xFx8Q/+zTI9ALMhBwVN0RxBh/03Su1OhkoC6zvhZVKf8pPJlvpw C3vbuL7q9c1j8DT18aFhVRB4fIgz3wTG/T7LZfXx67uQRfjdsSzK3iYIYQC5A52OXDkx UD5NZEovVxpYVRWZ4SXG36gWVEs0xLLKLScTefqwSi5QRZHMKdmjNkgDXRLg7/bx9h4Z 8AzFftrCLoeWe5eo6g3AB/JyZJ2v38oWXhiE/gbmbHhJOy8CwoEseSxn6e7NyCaXhdHJ XQ9Q== X-Gm-Message-State: ACgBeo1JqkrOm+kvkDu+wJE8bez2H1EEDYRvEHDSmtROTQFSR3ZFsF53 R10LMKRptMJwG/fftuxKS28= X-Google-Smtp-Source: AA6agR6wz/wRqsLGA1VDFCnrcJ6RF79Yt/qicnNT11CsJOqIpgO2RVF7xPfIkEvuXilrG2DkywD5VA== X-Received: by 2002:a17:902:9b98:b0:176:70e1:1f86 with SMTP id y24-20020a1709029b9800b0017670e11f86mr34884976plp.60.1663137237143; Tue, 13 Sep 2022 23:33:57 -0700 (PDT) Received: from hyeyoo ([114.29.91.56]) by smtp.gmail.com with ESMTPSA id o9-20020a62cd09000000b0053e199aa99bsm9033475pfg.220.2022.09.13.23.33.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Sep 2022 23:33:56 -0700 (PDT) Date: Wed, 14 Sep 2022 15:33:50 +0900 From: Hyeonggon Yoo <42.hyeyoo@gmail.com> To: Vlastimil Babka Cc: kernel test robot , lkp@lists.01.org, lkp@intel.com, Joel Fernandes , linux-mm@kvack.org, rcu@vger.kernel.org, paulmck@kernel.org, Alexey Dobriyan , Matthew Wilcox Subject: Re: [mm/sl[au]b] 3c4cafa313: canonical_address#:#[##] Message-ID: References: <20220906074548.GA72649@inn2.lkp.intel.com> <208c1757-5edd-fd42-67d4-1940cc43b50f@intel.com> <416149c0-1e18-0e00-d116-dd3738957556@suse.cz> <3d178109-5981-f4ee-8fe5-4f1d0c557ed2@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Fri, Sep 09, 2022 at 11:16:51PM +0200, Vlastimil Babka wrote: > On 9/9/22 16:32, Hyeonggon Yoo wrote: > > On Fri, Sep 09, 2022 at 03:44:19PM +0200, Vlastimil Babka wrote: > >> On 9/9/22 13:05, Hyeonggon Yoo wrote: > >> >> ----8<---- > >> >> From d6f9fbb33b908eb8162cc1f6ce7f7c970d0f285f Mon Sep 17 00:00:00 2001 > >> >> From: Vlastimil Babka > >> >> Date: Fri, 9 Sep 2022 12:03:10 +0200 > >> >> Subject: [PATCH 2/3] mm/migrate: make isolate_movable_page() skip slab pages > >> >> > >> >> In the next commit we want to rearrange struct slab fields to allow a > >> >> larger rcu_head. Afterwards, the page->mapping field will overlap > >> >> with SLUB's "struct list_head slab_list", where the value of prev > >> >> pointer can become LIST_POISON2, which is 0x122 + POISON_POINTER_DELTA. > >> >> Unfortunately the bit 1 being set can confuse PageMovable() to be a > >> >> false positive and cause a GPF as reported by lkp [1]. > >> >> > >> >> To fix this, make isolate_movable_page() skip pages with the PageSlab > >> >> flag set. This is a bit tricky as we need to add memory barriers to SLAB > >> >> and SLUB's page allocation and freeing, and their counterparts to > >> >> isolate_movable_page(). > >> > > >> > Hello, I just took a quick grasp, > >> > Is this approach okay with folio_test_anon()? > >> > >> Not if used on a completely random page as compaction scanners can, but > >> relies on those being first tested for PageLRU or coming from a page table > >> lookup etc. > >> Not ideal huh. Well I could improve also by switching 'next' and 'slabs' > >> field and relying on the fact that the value of LIST_POISON2 doesn't include > >> 0x1, just 0x2. > > > > What about swapping counters and freelist? > > freelist should be always aligned. > > Great suggestion, thanks! > > Had to deal with SLAB too as there was list_head.prev also aliasing > page->mapping. Wanted to use freelist as well, but turns out it's not > aligned, so had to use s_mem instead. > > The patch that isolate_movable_page() skip slab pages was thus dropped. The > result is in slab.git below and if nothing blows up, will restore it to -next > > https://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab.git/log/?h=for-6.1/fit_rcu_head I realized that there is also relevant comment in include/linux/mm_types.h: > 62 * SLUB uses cmpxchg_double() to atomically update its freelist and counters. > 63 * That requires that freelist & counters in struct slab be adjacent and > 64 * double-word aligned. Because struct slab currently just reinterprets the > 65 * bits of struct page, we align all struct pages to double-word boundaries, > 66 * and ensure that 'freelist' is aligned within struct slab. > 67 */ Also we may add a comment, something like this? --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -79,6 +79,9 @@ struct page { * WARNING: bit 0 of the first word is used for PageTail(). That * means the other users of this union MUST NOT use the bit to * avoid collision and false-positive PageTail(). + * + * WARNING: lower two bits of third word is used for PAGE_MAPPING_FLAGS. + * using those bits can lead compaction code to general protection fault. */ union { struct { /* Page cache and anonymous pages */ -- Thanks, Hyeonggon