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

Kirill A. Shutemov
2015-02-16T15:39:58Z

On Thu, Feb 12, 2015 at 04:10:21PM -0500, Rik van Riel wrote:
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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
> }

Okay, this is probably confusing: do_page_add_anon_rmap() already had one
of arguments called 'exclusive'. It indicates if the page is exclusively
owned by the current process. And I needed also to indicate if we need to
handle the page as a compound or not. I've reused the same argument and
converted it to set bit-flags: bit 0 is exclusive, bit 1 - 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.

I can convert these compound booleans to enums if you want. I'm personally
not sure that if will bring much value.

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Kirill A. Shutemov