Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932287AbbFPW3A (ORCPT ); Tue, 16 Jun 2015 18:29:00 -0400 Received: from g4t3425.houston.hp.com ([15.201.208.53]:3711 "EHLO g4t3425.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754418AbbFPW2w (ORCPT ); Tue, 16 Jun 2015 18:28:52 -0400 From: Toshi Kani To: akpm@linux-foundation.org Cc: kirill.shutemov@linux.intel.com, willy@linux.intel.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-nvdimm@ml01.01.org, linux-kernel@vger.kernel.org, Toshi Kani Subject: [PATCH] mm: Fix MAP_POPULATE and mlock() for DAX Date: Tue, 16 Jun 2015 16:28:30 -0600 Message-Id: <1434493710-11138-1-git-send-email-toshi.kani@hp.com> X-Mailer: git-send-email 1.9.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2236 Lines: 65 DAX has the following issues in a shared or read-only private mmap'd file. - mmap(MAP_POPULATE) does not pre-fault - mlock() fails with -ENOMEM DAX uses VM_MIXEDMAP for mmap'd files, which do not have struct page associated with the ranges. Both MAP_POPULATE and mlock() call __mm_populate(), which in turn calls __get_user_pages(). Because __get_user_pages() requires a valid page returned from follow_page_mask(), MAP_POPULATE and mlock(), i.e. FOLL_POPULATE, fail in the first page. Change __get_user_pages() to proceed FOLL_POPULATE when the translation is set but its page does not exist (-EFAULT), and @pages is not requested. With that, MAP_POPULATE and mlock() set translations to the requested range and complete successfully. MAP_POPULATE still provides a major performance improvement to DAX as it will avoid page faults during initial access to the pages. mlock() continues to set VM_LOCKED to vma and populate the range. Since there is no struct page, the range is pinned without marking pages mlocked. Note, MAP_POPULATE and mlock() already work for a write-able private mmap'd file on DAX since populate_vma_page_range() breaks COW, which allocates page caches. Signed-off-by: Toshi Kani --- mm/gup.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/mm/gup.c b/mm/gup.c index 6297f6b..16d536f 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -490,8 +490,20 @@ retry: } BUG(); } - if (IS_ERR(page)) + if (IS_ERR(page)) { + /* + * No page may be associated with VM_MIXEDMAP. Proceed + * FOLL_POPULATE when the translation is set but its + * page does not exist (-EFAULT), and @pages is not + * requested by the caller. + */ + if ((PTR_ERR(page) == -EFAULT) && (!pages) && + (gup_flags & FOLL_POPULATE) && + (vma->vm_flags & VM_MIXEDMAP)) + goto next_page; + return i ? i : PTR_ERR(page); + } if (pages) { pages[i] = page; flush_anon_page(vma, page, start); -- 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/