linux-kernel - Re: [PATCH v3 10/12] mm/gup: /proc/vmstat: pin_user_pages (FOLL

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Message-ID: <20200203213022.rltjlohvaswk32ln@box.shutemov.name>
Date:   Tue, 4 Feb 2020 00:30:22 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jonathan Corbet <corbet@....net>,
        Jérôme Glisse <jglisse@...hat.com>,
        Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Shuah Khan <shuah@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 10/12] mm/gup: /proc/vmstat: pin_user_pages (FOLL_PIN)
 reporting

On Mon, Feb 03, 2020 at 01:04:04PM -0800, John Hubbard wrote:
> On 2/3/20 5:53 AM, Kirill A. Shutemov wrote:
> > On Fri, Jan 31, 2020 at 07:40:27PM -0800, John Hubbard wrote:
> >> diff --git a/mm/gup.c b/mm/gup.c
> >> index c10d0d051c5b..9fe61d15fc0e 100644
> >> --- a/mm/gup.c
> >> +++ b/mm/gup.c
> >> @@ -29,6 +29,19 @@ struct follow_page_context {
> >>  	unsigned int page_mask;
> >>  };
> >>  
> >> +#ifdef CONFIG_DEBUG_VM
> > 
> > Why under CONFIG_DEBUG_VM? There's nothing about this in the cover letter.
> > 
> 
> Early on, gup_benchmark showed a really significant slowdown from using these 
> counters. And I don't doubt that it's still the case.
> 
> I'll re-measure and add a short summary and a few numbers to the patch commit
> description, and to the v4 cover letter.

Looks like you'll show zeros for these counters if debug is off. It can be
confusing to the user. I think these counters should go away if you don't
count them.

-- 
 Kirill A. Shutemov