From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: MIME-Version: 1.0 In-Reply-To: <1449092226.31589.50.camel@hpe.com> References: <1448309082-20851-1-git-send-email-toshi.kani@hpe.com> <1449022764.31589.24.camel@hpe.com> <1449078237.31589.30.camel@hpe.com> <1449084362.31589.37.camel@hpe.com> <1449086521.31589.39.camel@hpe.com> <1449087125.31589.45.camel@hpe.com> <1449092226.31589.50.camel@hpe.com> Date: Wed, 2 Dec 2015 12:54:05 -0800 Message-ID: Subject: Re: [PATCH] mm: Fix mmap MAP_POPULATE for DAX pmd mapping From: Dan Williams To: Toshi Kani Cc: Andrew Morton , "Kirill A. Shutemov" , Matthew Wilcox , Ross Zwisler , mauricio.porto@hpe.com, Linux MM , linux-fsdevel , "linux-nvdimm@lists.01.org" , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: On Wed, Dec 2, 2015 at 1:37 PM, Toshi Kani wrote: > On Wed, 2015-12-02 at 11:57 -0800, Dan Williams wrote: [..] >> The whole point of __get_user_page_fast() is to avoid the overhead of >> taking the mm semaphore to access the vma. _PAGE_SPECIAL simply tells >> __get_user_pages_fast that it needs to fallback to the >> __get_user_pages slow path. > > I see. Then, I think gup_huge_pmd() can simply return 0 when !pfn_valid(), > instead of VM_BUG_ON. Is pfn_valid() a reliable check? It seems to be based on a max_pfn per node... what happens when pmem is located below that point. I haven't been able to convince myself that we won't get false positives, but maybe I'm missing something. -- 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