linux-kernel - Re: [PATCH v5 10/12] mm/gup: /proc/vmstat: pin_user_pages (FOLL

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Message-ID: <7fcc15f4-e548-78bc-788d-f93293a1be74@nvidia.com>
Date:   Mon, 10 Feb 2020 09:07:07 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Jan Kara <jack@...e.cz>
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>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jonathan Corbet <corbet@....net>,
        Jérôme Glisse <jglisse@...hat.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        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 v5 10/12] mm/gup: /proc/vmstat: pin_user_pages (FOLL_PIN)
 reporting

On 2/10/20 2:16 AM, Jan Kara wrote:
> On Thu 06-02-20 19:37:33, John Hubbard wrote:
>> @@ -2258,6 +2268,8 @@ static int record_subpages(struct page *page, unsigned long addr,
>>   
>>   static void put_compound_head(struct page *page, int refs, unsigned int flags)
>>   {
>> +	int orig_refs = refs;
>> +
>>   	if (flags & FOLL_PIN) {
>>   		if (hpage_pincount_available(page))
>>   			hpage_pincount_sub(page, refs);
>> @@ -2273,6 +2285,8 @@ static void put_compound_head(struct page *page, int refs, unsigned int flags)
>>   	if (refs > 1)
>>   		page_ref_sub(page, refs - 1);
>>   	put_page(page);
>> +
>> +	mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, orig_refs);
>>   }
> 
> Still not quite happy about this :) Now you update NR_FOLL_PIN_RELEASED
> even if 'flags' don't have FOLL_PIN set. You need to have the
> mod_node_page_state() inside the "if (flags & FOLL_PIN)" branch above...
> 
> 									Honza

Arggh, yes that's true. Thanks for catching that, will fix in v6.


thanks,
-- 
John Hubbard
NVIDIA