From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-f182.google.com (mail-we0-f182.google.com [74.125.82.182]) by kanga.kvack.org (Postfix) with ESMTP id 2B5E96B0032 for ; Wed, 21 Jan 2015 05:16:01 -0500 (EST) Received: by mail-we0-f182.google.com with SMTP id l61so16934292wev.13 for ; Wed, 21 Jan 2015 02:16:00 -0800 (PST) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id f13si37558315wjq.94.2015.01.21.02.16.00 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 21 Jan 2015 02:16:00 -0800 (PST) Message-ID: <54BF7C5E.6050503@suse.cz> Date: Wed, 21 Jan 2015 11:15:58 +0100 From: Vlastimil Babka MIME-Version: 1.0 Subject: Re: [PATCH] mm: Don't offset memmap for flatmem References: <1421804273-29947-1-git-send-email-lauraa@codeaurora.org> In-Reply-To: <1421804273-29947-1-git-send-email-lauraa@codeaurora.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Laura Abbott , Srinivas Kandagatla , linux-arm-kernel@lists.infradead.org, Russell King - ARM Linux , ssantosh@kernel.org, Andrew Morton Cc: Kevin Kilman , Stephen Boyd , Arnd Bergman , Kumar Gala , linux-mm@kvack.org On 01/21/2015 02:37 AM, Laura Abbott wrote: > Srinivas Kandagatla reported bad page messages when trying to > remove the bottom 2MB on an ARM based IFC6410 board > > BUG: Bad page state in process swapper pfn:fffa8 > page:ef7fb500 count:0 mapcount:0 mapping: (null) index:0x0 > flags: 0x96640253(locked|error|dirty|active|arch_1|reclaim|mlocked) > page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set > bad because of flags: > flags: 0x200041(locked|active|mlocked) > Modules linked in: > CPU: 0 PID: 0 Comm: swapper Not tainted 3.19.0-rc3-00007-g412f9ba-dirty #816 > Hardware name: Qualcomm (Flattened Device Tree) > [] (unwind_backtrace) from [] (show_stack+0x20/0x24) > [] (show_stack) from [] (dump_stack+0x80/0x9c) > [] (dump_stack) from [] (bad_page+0xc8/0x128) > [] (bad_page) from [] (free_pages_prepare+0x168/0x1e0) > [] (free_pages_prepare) from [] (free_hot_cold_page+0x3c/0x174) > [] (free_hot_cold_page) from [] (__free_pages+0x54/0x58) > [] (__free_pages) from [] (free_highmem_page+0x38/0x88) > [] (free_highmem_page) from [] (mem_init+0x240/0x430) > [] (mem_init) from [] (start_kernel+0x1e4/0x3c8) > [] (start_kernel) from [<80208074>] (0x80208074) > Disabling lock debugging due to kernel taint > > Removing the lower 2MB made the start of the lowmem zone to no longer > be page block aligned. IFC6410 uses CONFIG_FLATMEM where > alloc_node_mem_map allocates memory for the mem_map. alloc_node_mem_map > will offset for unaligned nodes with the assumption the pfn/page > translation functions will account for the offset. The functions for > CONFIG_FLATMEM do not offset however, resulting in overrunning > the memmap array. Just use the allocated memmap without any offset > when running with CONFIG_FLATMEM to avoid the overrun. > > Signed-off-by: Laura Abbott > Reported-by: Srinivas Kandagatla > --- > Srinivas, can you test this version of the patch? > --- > mm/page_alloc.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 7633c50..33cef00 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -5014,6 +5014,7 @@ static void __init_refok alloc_node_mem_map(struct pglist_data *pgdat) > if (!pgdat->node_mem_map) { > unsigned long size, start, end; > struct page *map; > + unsigned long offset = 0; > > /* > * The zone's endpoints aren't required to be MAX_ORDER > @@ -5021,6 +5022,8 @@ static void __init_refok alloc_node_mem_map(struct pglist_data *pgdat) > * for the buddy allocator to function correctly. > */ > start = pgdat->node_start_pfn & ~(MAX_ORDER_NR_PAGES - 1); > + if (!IS_ENABLED(CONFIG_FLATMEM)) > + offset = pgdat->node_start_pfn - start; > end = pgdat_end_pfn(pgdat); > end = ALIGN(end, MAX_ORDER_NR_PAGES); > size = (end - start) * sizeof(struct page); > @@ -5028,7 +5031,7 @@ static void __init_refok alloc_node_mem_map(struct pglist_data *pgdat) > if (!map) > map = memblock_virt_alloc_node_nopanic(size, > pgdat->node_id); > - pgdat->node_mem_map = map + (pgdat->node_start_pfn - start); > + pgdat->node_mem_map = map + offset; Hmm, by this patch, you have changed not only mem_map, but also node_mem_map itself. So the result of pgdat_page_nr() defined in mmzone.h will now be different in the CONFIG_FLAT_NODE_MEM_MAP case? #ifdef CONFIG_FLAT_NODE_MEM_MAP #define pgdat_page_nr(pgdat, pagenr) ((pgdat)->node_mem_map + (pagenr)) #else #define pgdat_page_nr(pgdat, pagenr) pfn_to_page((pgdat)->node_start_pfn + (pagenr)) #define nid_page_nr(nid, pagenr) pgdat_page_nr(NODE_DATA(nid),(pagenr)) It appears that nobody uses pgdat_page_nr, except nid_page_nr, which nobody uses. But better not leave it broken, and there's also some arch-specific code looking at node_mem_map directly (although not sure if this particular combination of CONFIG_ parameters applies there). So it seems to me we should rather apply the offset to node_mem_map in any case, but not apply it (i.e. subtract it back) to mem_map for !CONFIG_FLATMEM? Thanks. > } > #ifndef CONFIG_NEED_MULTIPLE_NODES > /* > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org