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Thu, 7 Jun 2018 18:47:27 -0400 Received: from mga02.intel.com ([134.134.136.20]:25665 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751521AbeFGWrZ (ORCPT ); Thu, 7 Jun 2018 18:47:25 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 07 Jun 2018 15:47:25 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.49,488,1520924400"; d="scan'208";a="62750857" Received: from ray.jf.intel.com (HELO [10.7.201.24]) ([10.7.201.24]) by orsmga001.jf.intel.com with ESMTP; 07 Jun 2018 15:47:25 -0700 Subject: Re: [PATCH v4 4/4] mm/sparse: Optimize memmap allocation during sparse_init() To: Baoquan He , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, pagupta@redhat.com References: <20180521101555.25610-1-bhe@redhat.com> <20180521101555.25610-5-bhe@redhat.com> Cc: linux-mm@kvack.org, kirill.shutemov@linux.intel.com From: Dave Hansen Openpgp: preference=signencrypt Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <20180521101555.25610-5-bhe@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > @@ -297,8 +298,8 @@ void __init sparse_mem_maps_populate_node(struct page **map_map, > if (!present_section_nr(pnum)) > continue; > > - map_map[pnum] = sparse_mem_map_populate(pnum, nodeid, NULL); > - if (map_map[pnum]) > + map_map[nr_consumed_maps] = sparse_mem_map_populate(pnum, nodeid, NULL); > + if (map_map[nr_consumed_maps++]) > continue; ... This looks wonky. This seems to say that even if we fail to sparse_mem_map_populate() (it returns NULL), we still consume a map. Is that right? > /* fallback */ > + nr_consumed_maps = 0; > for (pnum = pnum_begin; pnum < pnum_end; pnum++) { > struct mem_section *ms; > > if (!present_section_nr(pnum)) > continue; > - map_map[pnum] = sparse_mem_map_populate(pnum, nodeid, NULL); > - if (map_map[pnum]) > + map_map[nr_consumed_maps] = sparse_mem_map_populate(pnum, nodeid, NULL); > + if (map_map[nr_consumed_maps++]) > continue; Same questionable pattern as above... > #ifdef CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER > - size2 = sizeof(struct page *) * NR_MEM_SECTIONS; > + size2 = sizeof(struct page *) * nr_present_sections; > map_map = memblock_virt_alloc(size2, 0); > if (!map_map) > panic("can not allocate map_map\n"); > @@ -586,27 +594,44 @@ void __init sparse_init(void) > sizeof(map_map[0])); > #endif > > + /* The numner of present sections stored in nr_present_sections "number"? Also, this is not correct comment CodingStyle. > + * are kept the same since mem sections are marked as present in > + * memory_present(). Are you just trying to say that we are not making sections present here? > In this for loop, we need check which sections > + * failed to allocate memmap or usemap, then clear its > + * ->section_mem_map accordingly. During this process, we need > + * increase 'alloc_usemap_and_memmap' whether its allocation of > + * memmap or usemap failed or not, so that after we handle the i-th > + * memory section, can get memmap and usemap of (i+1)-th section > + * correctly. */ I'm really scratching my head over this comment. For instance "increase 'alloc_usemap_and_memmap'" doesn't make any sense to me. How do you increase a function? I wonder if you could give that comment another shot.