From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from aserp1040.oracle.com (aserp1040.oracle.com [141.146.126.69]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3xWH9L02mmzDqh5 for ; Mon, 14 Aug 2017 23:52:21 +1000 (AEST) Subject: Re: [v6 05/15] mm: don't accessed uninitialized struct pages To: Michal Hocko Cc: linux-kernel@vger.kernel.org, sparclinux@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-arm-kernel@lists.infradead.org, x86@kernel.org, kasan-dev@googlegroups.com, borntraeger@de.ibm.com, heiko.carstens@de.ibm.com, davem@davemloft.net, willy@infradead.org, ard.biesheuvel@linaro.org, will.deacon@arm.com, catalin.marinas@arm.com, sam@ravnborg.org References: <1502138329-123460-1-git-send-email-pasha.tatashin@oracle.com> <1502138329-123460-6-git-send-email-pasha.tatashin@oracle.com> <20170811093746.GF30811@dhcp22.suse.cz> <8444cb2b-b134-e9fc-a458-1ba7b22a8df1@oracle.com> <20170814114755.GI19063@dhcp22.suse.cz> From: Pasha Tatashin Message-ID: Date: Mon, 14 Aug 2017 09:51:12 -0400 MIME-Version: 1.0 In-Reply-To: <20170814114755.GI19063@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , >> mem_init() >> free_all_bootmem() >> free_low_memory_core_early() >> for_each_reserved_mem_region() >> reserve_bootmem_region() >> init_reserved_page() <- if this is deferred reserved page >> __init_single_pfn() >> __init_single_page() >> >> So, currently, we are using the value of page->flags to figure out if this >> page has been initialized while being part of deferred page, but this is not >> going to work for this project, as we do not zero the memory that is backing >> the struct pages, and size the value of page->flags can be anything. > > True, this is the initialization part I've missed in one of the previous > patches already. Would it be possible to only iterate over !reserved > memory blocks instead? Now that we discard all the metadata later it > should be quite easy to do for_each_memblock_type, no? Hi Michal, Clever suggestion to add a new iterator to go through unreserved existing memory, I do not think there is this iterator available, so it would need to be implemented, using similar approach to what I have done with a call back. However, there is a different reason, why I took this current approach. Daniel Jordan is working on a ktask support: https://lkml.org/lkml/2017/7/14/666 He and I discussed on how to multi-thread struct pages initialization within memory nodes using ktasks. Having this callback interface makes that multi-threading quiet easy, improving the boot performance further, with his prototype we saw x4-6 improvements (using 4-8 threads per node). Reducing the total time it takes to initialize all struct pages on machines with terabytes of memory to less than one second. Pasha