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

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Date:   Mon, 10 Feb 2020 11:16:29 +0100
From:   Jan Kara <jack@...e.cz>
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>,
        "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 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
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR