From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758848AbZIPMVm (ORCPT ); Wed, 16 Sep 2009 08:21:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758650AbZIPMVl (ORCPT ); Wed, 16 Sep 2009 08:21:41 -0400 Received: from mail-yx0-f171.google.com ([209.85.210.171]:46760 "EHLO mail-yx0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752798AbZIPMVk convert rfc822-to-8bit (ORCPT ); Wed, 16 Sep 2009 08:21:40 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=tcGsiHOk3iq4JfT7Dh9YIvxuS1g3J52nzPI+8y4qGwJ6pItUuoui/nbJ/o5QzYFweE dSXgvsmXfkPSICSTGQoxLbWRSmM5Ab/FQ6ap0m/NqC5NEC5UmNFG47v8a+wuIDm6jAsF XTfZ4T84KhZkU7te4rB/o06UUxJ/1ldjTSJGg= MIME-Version: 1.0 In-Reply-To: <20090915122632.GC31840@csn.ul.ie> References: <202cde0e0909132218k70c31a5u922636914e603ad4@mail.gmail.com> <20090915122632.GC31840@csn.ul.ie> Date: Thu, 17 Sep 2009 00:21:42 +1200 Message-ID: <202cde0e0909160521v41a0d9f2wb1e4fe1e379e8971@mail.gmail.com> Subject: Re: [PATCH 2/3] Helper which returns the huge page at a given address (Take 3) From: Alexey Korolev To: Mel Gorman Cc: Eric Munson , Alexey Korolev , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 16, 2009 at 12:26 AM, Mel Gorman wrote: > On Mon, Sep 14, 2009 at 05:18:53PM +1200, Alexey Korolev wrote: >> This patch provides helper function which returns the huge page at a >> given address for population before the page has been faulted. >> It is possible to call hugetlb_get_user_page function in file mmap >> procedure to get pages before they have been requested by user level. >> > > Worth spelling out that this is similar in principal to get_user_pages() > but not as painful to use in this specific context. > Right. I'll do this. Seems it is important to clearly mention that this function do not introduce new functionality. >> include/linux/hugetlb.h |    3 +++ >> mm/hugetlb.c            |   23 +++++++++++++++++++++++ >> 2 files changed, 26 insertions(+) >> >> --- >> Signed-off-by: Alexey Korolev > > Patch formatting nit. > > diffstat goes below the --- and signed-off-bys go above it. > Right. To be fixed. >> >> +/* >> + * hugetlb_get_user_page returns the page at a given address for population >> + * before the page has been faulted. >> + */ >> +struct page *hugetlb_get_user_page(struct vm_area_struct *vma, >> +                                 unsigned long address) >> +{ > > Your leader and comments say that the function can be used before the pages > have been faulted. It would presumably require that this function be called > from within a mmap() handler. > > What is happening because you call follow_hugetlb_page() is that the pages > get faulted as part of your mmap() operation. This might make the overall > operation more expensive than you expected. I don't know if what you really > intended was to allocate the huge page, insert it into the page cache and > have it faulted later if the process actually references the page. > > Similarly the leader and comments imply that you expect this to be > called as part of the mmap() operation. However, nothing would appear to > prevent the driver calling this function once the page is already > faulted. Is this intentional? The implication was not intende. You are correct, the function can be called later. The leader and comment can be rewritten to make this clear. >> +     int ret; >> +     int cnt = 1; >> +     struct page *pg; >> +     struct hstate *h = hstate_vma(vma); >> + >> +     address = address & huge_page_mask(h); >> +     ret = follow_hugetlb_page(vma->vm_mm, vma, &pg, >> +                             NULL, &address, &cnt, 0, 0); >> +     if (ret < 0) >> +             return ERR_PTR(ret); >> +     put_page(pg); >> + >> +     return pg; >> +} > > I think the caller should be responsible for calling put_page().  Otherwise > there is an outside chance that the page would disappear from you unexpectedly > depending on exactly how the driver was implemented. It would also > behave slightly more like get_user_pages(). > Correct. Lets have behaviour similar to get_user_pages in order to prevent misunderstanding. Put_page will be removed. Thank you very much for review. Now I am about to clear out the mistakes and will pay a lot more attention to patch descriptions and comments. Thanks, Alexey