linux-kernel - Re: [PATCHv3 04/24] rmap: add argument to charge compound page

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Date:	Thu, 12 Feb 2015 16:10:21 -0500
From:	Rik van Riel <riel@...hat.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hughd@...gle.com>
CC:	Dave Hansen <dave.hansen@...el.com>, Mel Gorman <mgorman@...e.de>,
	Vlastimil Babka <vbabka@...e.cz>,
	Christoph Lameter <cl@...two.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Steve Capper <steve.capper@...aro.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Jerome Marchand <jmarchan@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv3 04/24] rmap: add argument to charge compound page

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On 02/12/2015 11:18 AM, Kirill A. Shutemov wrote:

> +++ b/include/linux/rmap.h @@ -168,16 +168,24 @@ static inline void
> anon_vma_merge(struct vm_area_struct *vma,
> 
> struct anon_vma *page_get_anon_vma(struct page *page);
> 
> +/* flags for do_page_add_anon_rmap() */ +enum { +	RMAP_EXCLUSIVE =
> 1, +	RMAP_COMPOUND = 2, +};

Always a good idea to name things. However, "exclusive" is
not that clear to me. Given that the argument is supposed
to indicate whether we map a single or a compound page,
maybe the names in the enum could just be SINGLE and COMPOUND?

Naming the enum should make it clear enough what it does:

 enum rmap_page {
      SINGLE = 0,
      COMPOUND
 }

> +++ b/kernel/events/uprobes.c @@ -183,7 +183,7 @@ static int
> __replace_page(struct vm_area_struct *vma, unsigned long addr, goto
> unlock;
> 
> get_page(kpage); -	page_add_new_anon_rmap(kpage, vma, addr); +
> page_add_new_anon_rmap(kpage, vma, addr, false); 
> mem_cgroup_commit_charge(kpage, memcg, false); 
> lru_cache_add_active_or_unevictable(kpage, vma);

Would it make sense to use the name in the argument to that function,
too?

I often find it a lot easier to see what things do if they use symbolic
names, rather than by trying to remember what each boolean argument to
a function does.

- -- 
All rights reversed
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