Messages in this thread | | | Date | Thu, 05 Jan 2012 11:28:31 -0500 | From | Naoya Horiguchi <> | Subject | Re: [PATCH 1/4] pagemap: avoid splitting thp when reading /proc/pid/pagemap |
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On Wed, Jan 04, 2012 at 03:50:42PM -0800, Andrew Morton wrote: > On Wed, 21 Dec 2011 17:23:45 -0500 > Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> wrote: > > > Thp split is not necessary if we explicitly check whether pmds are > > mapping thps or not. This patch introduces the check and the code > > to generate pagemap entries for pmds mapping thps, which results in > > less performance impact of pagemap on thp. > > > > > > ... > > The type choices seem odd: > > > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE > > +static u64 thp_pte_to_pagemap_entry(pte_t pte, int offset) > > +{ > > + u64 pme = 0; > > Why are these u64?
I guess (I just copied this type choice from other *pte_to_pagemap_entry() type functions) it's because each entry in /proc/pid/pagemap is in fixed sized (64 bit) format as described in the comment above pagemap_read().
> Should we have a pme_t, matching pte_t, pmd_t, etc?
Yes, it makes code's meaning clearer.
> > > + if (pte_present(pte)) > > + pme = PM_PFRAME(pte_pfn(pte) + offset) > > + | PM_PSHIFT(PAGE_SHIFT) | PM_PRESENT; > > + return pme; > > +} > > +#else > > +static inline u64 thp_pte_to_pagemap_entry(pte_t pte, int offset) > > +{ > > + return 0; > > +} > > +#endif > > + > > static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, > > struct mm_walk *walk) > > { > > @@ -665,14 +684,34 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, > > struct pagemapread *pm = walk->private; > > pte_t *pte; > > int err = 0; > > - > > - split_huge_page_pmd(walk->mm, pmd); > > + u64 pfn = PM_NOT_PRESENT; > > Again, why a u64? pfn's are usually unsigned long.
I think variable's name 'pfn' is wrong rather than type choice because this variable stores pagemap entry which is not a pure pfn. There's room for improvement, so I'll try it in the next turn.
Thanks, Naoya
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