From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f71.google.com (mail-oi0-f71.google.com [209.85.218.71]) by kanga.kvack.org (Postfix) with ESMTP id 0224A6B0253 for ; Mon, 12 Sep 2016 13:29:19 -0400 (EDT) Received: by mail-oi0-f71.google.com with SMTP id h11so135043924oic.2 for ; Mon, 12 Sep 2016 10:29:18 -0700 (PDT) Received: from mail-it0-x236.google.com (mail-it0-x236.google.com. [2607:f8b0:4001:c0b::236]) by mx.google.com with ESMTPS id c11si4739034iof.66.2016.09.12.10.29.18 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 12 Sep 2016 10:29:18 -0700 (PDT) Received: by mail-it0-x236.google.com with SMTP id 186so20859174itf.0 for ; Mon, 12 Sep 2016 10:29:18 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20160912133536.1bdb57a9@roar.ozlabs.ibm.com> References: <147361509579.17004.5258725187329709824.stgit@dwillia2-desk3.amr.corp.intel.com> <20160912133536.1bdb57a9@roar.ozlabs.ibm.com> From: Dan Williams Date: Mon, 12 Sep 2016 10:29:17 -0700 Message-ID: Subject: Re: [RFC PATCH 1/2] mm, mincore2(): retrieve dax and tlb-size attributes of an address range Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Nicholas Piggin Cc: Linux MM , Andrea Arcangeli , Xiao Guangrong , Arnd Bergmann , "linux-nvdimm@lists.01.org" , linux-api@vger.kernel.org, Dave Hansen , "linux-kernel@vger.kernel.org" , Andrew Morton , "Kirill A. Shutemov" , linux-arch@vger.kernel.org On Sun, Sep 11, 2016 at 8:35 PM, Nicholas Piggin wrote: > On Sun, 11 Sep 2016 10:31:35 -0700 > Dan Williams wrote: > >> As evidenced by this bug report [1], userspace libraries are interested >> in whether a mapping is DAX mapped, i.e. no intervening page cache. >> Rather than using the ambiguous VM_MIXEDMAP flag in smaps, provide an >> explicit "is dax" indication as a new flag in the page vector populated >> by mincore. > > Can you cc linux-arch when adding new syscalls (or other such things that > need arch enablement). > > I wonder if the changelog for a new syscall should have a bit more grandeur. > Without seeing patch 2, you might not know this was a new syscall just by > reading the subject and changelog. Fair point, I'll beef up the documentation if this moves past an RFC. > mincore() defines other bits to be reserved, but I guess it probably breaks > things if you suddenly started using them. The new bits are left as zero unless an application explicitly asks for them, so an existing mincore() user shouldn't break. > It's a bit sad to introduce a new syscall for this and immediately use up > all bits that can be returned. Would it be a serious problem to return a > larger mask per page? Certainly one of the new request flags can indicate that the vector is made up of larger entries. -- 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