[PATCH] ARM: mm: enforce pageblock alignment when freeing memmap entries at init
From: Mel Gorman <hidden>
Date: 2011-01-26 08:29:16
On Thu, Jan 20, 2011 at 03:47:11PM -0800, Dima Zavin wrote:
On some machines, the nodes do not always start on pageblock boundaries. In these cases it is possible for free_unused_memmap to free mappings for pages inside a pageblock with otherwise valid pages. This presents problems for page migration since it operates on whole pageblocks at a time.
This patch is not aligning on a pageblock boundary - it's aligning on MAX_ORDER_NR_PAGES which is the boundary the buddy allocator works on. This is a minor but important nit as different assumptions are made about pageblocks and MAX_ORDER_NR_PAGES. Anyway; If the node is not starting on the MAX_ORDER boundary then node_start_pfn should also not be on the same boundary but the patch does not imply that this has been broken. If anything it appears at a glance that there is memmap *not* being freed because it was allocated on the MAX_ORDER_NR_PAGES boundary and only partially freed. The comment then is confusing because the function is freeing memmap but rounding down to free more of it ensures that all pages get a mapping? It's not clear at all to me what was broken or how this patch fixes it but bear in mind that it's rare I look at how ARM is initialised.
quoted hunk ↗ jump to hunk
Round down bank_start to pageblock boundary so that whole pageblocks always have valid mappings. Signed-off-by: Dima Zavin <redacted> --- arch/arm/mm/init.c | 6 +++++- 1 files changed, 5 insertions(+), 1 deletions(-)diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c index 5164069..98de5d8 100644 --- a/arch/arm/mm/init.c +++ b/arch/arm/mm/init.c@@ -418,7 +418,11 @@ static void __init free_unused_memmap(struct meminfo *mi) for_each_bank(i, mi) { struct membank *bank = &mi->bank[i]; - bank_start = bank_pfn_start(bank); + /* Round bank_start down to the start of a pageblock so that + * all pages in a pageblock always have a mapping. + */ + bank_start = round_down(bank_pfn_start(bank), + MAX_ORDER_NR_PAGES); /* * If we had a previous bank, and there is a space-- 1.7.3.1
-- Mel Gorman Linux Technology Center IBM Dublin Software Lab