From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f175.google.com (mail-ob0-f175.google.com [209.85.214.175]) by kanga.kvack.org (Postfix) with ESMTP id C42F46B0032 for ; Tue, 16 Jun 2015 18:28:53 -0400 (EDT) Received: by obbsn1 with SMTP id sn1so21433734obb.1 for ; Tue, 16 Jun 2015 15:28:53 -0700 (PDT) Received: from g4t3425.houston.hp.com (g4t3425.houston.hp.com. [15.201.208.53]) by mx.google.com with ESMTPS id t9si1427679oig.65.2015.06.16.15.28.52 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 16 Jun 2015 15:28:52 -0700 (PDT) From: 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> Sender: owner-linux-mm@kvack.org List-ID: 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@lists.01.org, linux-kernel@vger.kernel.org, Toshi Kani 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, 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