Messages in this thread | | | Date | Mon, 19 Dec 2011 14:16:17 -0500 | From | Naoya Horiguchi <> | Subject | Re: [RFC][PATCH 1/3] pagemap: avoid splitting thp when reading /proc/pid/pagemap |
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On Mon, Dec 19, 2011 at 10:48:17AM -0800, David Rientjes wrote: > On Mon, 19 Dec 2011, Naoya Horiguchi wrote: ... > > @@ -666,10 +685,33 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, > > pte_t *pte; > > int err = 0; > > > > - split_huge_page_pmd(walk->mm, pmd); > > - > > /* find the first VMA at or above 'addr' */ > > vma = find_vma(walk->mm, addr); > > + > > + spin_lock(&walk->mm->page_table_lock); > > pagemap_pte_range() could potentially be called a _lot_, so I'd recommend > optimizing this by checking for pmd_trans_huge() prior to taking > page_table_lock and then rechecking after grabbing it with likely().
OK, I'll try it. Similar logic is used on smaps_pte_range() and gather_pte_stats(), so I think it's better to write a separate patch for this optimization.
> > + if (pmd_trans_huge(*pmd)) { > > + if (pmd_trans_splitting(*pmd)) { > > + spin_unlock(&walk->mm->page_table_lock); > > + wait_split_huge_page(vma->anon_vma, pmd); > > + } else { > > + u64 pfn = PM_NOT_PRESENT; > > This doesn't need to be initialized and it would probably be better to > declare "pfn" at the top-level of this function since it's later used for > the non-thp case.
Agreed. I unify two declarations of "pfn" at the beginning of the function.
Thank you for nice feedback. Naoya
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