Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755100AbXJCPsb (ORCPT ); Wed, 3 Oct 2007 11:48:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756821AbXJCPsR (ORCPT ); Wed, 3 Oct 2007 11:48:17 -0400 Received: from e4.ny.us.ibm.com ([32.97.182.144]:55501 "EHLO e4.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756135AbXJCPsQ (ORCPT ); Wed, 3 Oct 2007 11:48:16 -0400 From: Adam Litke Subject: [PATCH] hugetlb: Fix pool resizing corner case Date: Wed, 03 Oct 2007 08:47:48 -0700 To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Adam Litke Message-Id: <20071003154748.19516.90317.stgit@kernel> Content-Type: text/plain; charset=utf-8; format=fixed Content-Transfer-Encoding: 8bit User-Agent: StGIT/0.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2285 Lines: 63 When shrinking the size of the hugetlb pool via the nr_hugepages sysctl, we are careful to keep enough pages around to satisfy reservations. But the calculation is flawed for the following scenario: Action Pool Counters (Total, Free, Resv) ====== ============= Set pool to 1 page 1 1 0 Map 1 page MAP_PRIVATE 1 1 0 Touch the page to fault it in 1 0 0 Set pool to 3 pages 3 2 0 Map 2 pages MAP_SHARED 3 2 2 Set pool to 2 pages 2 1 2 <-- Mistake, should be 3 2 2 Touch the 2 shared pages 2 0 1 <-- Program crashes here The last touch above will terminate the process due to lack of huge pages. This patch corrects the calculation so that it factors in pages being used for private mappings. Andrew, this is a standalone fix suitable for mainline. It is also now corrected in my latest dynamic pool resizing patchset which I will send out soon. Signed-off-by: Adam Litke --- mm/hugetlb.c | 6 +++--- 1 files changed, 3 insertions(+), 3 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 84c795e..7af3908 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -224,14 +224,14 @@ static void try_to_free_low(unsigned long count) for (i = 0; i < MAX_NUMNODES; ++i) { struct page *page, *next; list_for_each_entry_safe(page, next, &hugepage_freelists[i], lru) { + if (count >= nr_huge_pages) + return; if (PageHighMem(page)) continue; list_del(&page->lru); update_and_free_page(page); free_huge_pages--; free_huge_pages_node[page_to_nid(page)]--; - if (count >= nr_huge_pages) - return; } } } @@ -251,7 +251,7 @@ static unsigned long set_max_huge_pages(unsigned long count) return nr_huge_pages; spin_lock(&hugetlb_lock); - count = max(count, resv_huge_pages); + count = max(count, resv_huge_pages + nr_huge_pages - free_huge_pages); try_to_free_low(count); while (count < nr_huge_pages) { struct page *page = dequeue_huge_page(NULL, 0); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/