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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.2.1 Subject: Re: [mm/sl[au]b] 3c4cafa313: canonical_address#:#[##] Content-Language: en-US To: Hyeonggon Yoo <42.hyeyoo@gmail.com> 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 References: <20220906074548.GA72649@inn2.lkp.intel.com> <208c1757-5edd-fd42-67d4-1940cc43b50f@intel.com> <416149c0-1e18-0e00-d116-dd3738957556@suse.cz> From: Vlastimil Babka In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1662731061; a=rsa-sha256; cv=none; b=G5/tl2KbLewPuX19nld4WlJX9p6ZH8AYVOsqdiY/mZSVUSihe4Iml6FeTT3uc5/ROWD5nU zxgqGqt9cOWwpsFj1vkZY4GvlpmsF+A6B9TypEsAGaUWUL+27lxubyAnY1kiHz7jppMY5u hx+bIfyBUxaBYc1CFQ+y6xBNOp+DMGQ= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=f+yVDyqD; 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spf=pass (imf18.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.28 as permitted sender) smtp.mailfrom=vbabka@suse.cz; dmarc=none X-Rspam-User: X-Rspamd-Server: rspam06 X-Stat-Signature: d4wzaj5tzkqddznnp5hpn39ktbfzp41k X-HE-Tag: 1662731061-258075 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 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.