From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f178.google.com (mail-pd0-f178.google.com [209.85.192.178]) by kanga.kvack.org (Postfix) with ESMTP id 732C36B0038 for ; Fri, 10 Oct 2014 01:24:22 -0400 (EDT) Received: by mail-pd0-f178.google.com with SMTP id y10so992397pdj.37 for ; Thu, 09 Oct 2014 22:24:22 -0700 (PDT) Received: from mail-pa0-x22e.google.com (mail-pa0-x22e.google.com [2607:f8b0:400e:c03::22e]) by mx.google.com with ESMTPS id zo6si2742548pac.3.2014.10.09.22.24.20 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 09 Oct 2014 22:24:20 -0700 (PDT) Received: by mail-pa0-f46.google.com with SMTP id fa1so1045899pad.33 for ; Thu, 09 Oct 2014 22:24:20 -0700 (PDT) Date: Fri, 10 Oct 2014 21:21:08 +0800 From: Fengwei Yin Subject: Re: [PATCH] smaps should deal with huge zero page exactly same as normal zero page Message-ID: <20141010132027.GB25038@gmail.com> References: <5436B98E.1070407@intel.com> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="GID0FwUMdk1T2AWN" Content-Disposition: inline In-Reply-To: <5436B98E.1070407@intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: LKML , linux-mm@kvack.org, fengguang.wu@intel.com, "Kirill A. Shutemov" --GID0FwUMdk1T2AWN Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Thu, Oct 09, 2014 at 09:36:30AM -0700, Dave Hansen wrote: > On 10/09/2014 02:19 AM, Fengwei Yin wrote: > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > > index 80ca4fb..8550b27 100644 > > --- a/fs/proc/task_mmu.c > > +++ b/fs/proc/task_mmu.c > > @@ -476,7 +476,7 @@ static void smaps_pte_entry(pte_t ptent, unsigned long addr, > > mss->nonlinear += ptent_size; > > } > > > > - if (!page) > > + if (!page || is_huge_zero_page(page)) > > return; > > This really seems like a bit of a hack. A normal (small) zero page > won't make it to this point because of the vm_normal_page() check in > smaps_pte_entry() which hits the _PAGE_SPECIAL bit in the pte. > > Is there a reason we can't set _PAGE_SPECIAL on the huge_zero_page ptes? > If we did that, we wouldn't need a special case here. > > If we can't do that for some reason, can we at least teach > vm_normal_page() about the huge_zero_page in some other way? I suppose _PAGE_SPECIAL can't work. Two reasons: 1. Not all arch have HAVE_PTE_SPECIAL set. So always need another way to handle the arch which has no PTE_SPECIAL. 2. _PAGE_SPECIAL is just for PTE now. If want to add it for huge page, we need to introduce pmd_mkspecial() thing which I don't think it's worth to do now (unless you want it. :)). Yes. We could move the check to vm_normal_page(). But it still needs export functions from huge_memory.c. Please check the new patch. > > > if (PageAnon(page)) > > @@ -516,7 +516,8 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, > > if (pmd_trans_huge_lock(pmd, vma, &ptl) == 1) { > > smaps_pte_entry(*(pte_t *)pmd, addr, HPAGE_PMD_SIZE, walk); > > spin_unlock(ptl); > > - mss->anonymous_thp += HPAGE_PMD_SIZE; > > + if (!is_huge_zero_pmd(*pmd)) > > + mss->anonymous_thp += HPAGE_PMD_SIZE; > > return 0; > > } > > How about we just move this hunk in to smaps_pte_entry()? Something > along these lines: > > ... > if (PageAnon(page)) { > mss->anonymous += ptent_size; > + if (PageTransHuge(page)) > + mss->anonymous_thp += ptent_size; > } Done. > > If we do that, plus teaching vm_normal_page() about huge_zero_pages, it > will help keep the hacks and the extra code due to huge pages to a miniumum. > > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > > index 63579cb..758f569 100644 > > --- a/include/linux/huge_mm.h > > +++ b/include/linux/huge_mm.h > > @@ -34,6 +34,10 @@ extern int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > > unsigned long addr, pgprot_t newprot, > > int prot_numa); > > > > +extern bool is_huge_zero_page(struct page *page); > > + > > +extern bool is_huge_zero_pmd(pmd_t pmd); > > + > > enum transparent_hugepage_flag { > > TRANSPARENT_HUGEPAGE_FLAG, > > TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > index d9a21d06..bedc3ae 100644 > > --- a/mm/huge_memory.c > > +++ b/mm/huge_memory.c > > @@ -173,12 +173,12 @@ static int start_khugepaged(void) > > static atomic_t huge_zero_refcount; > > static struct page *huge_zero_page __read_mostly; > > > > -static inline bool is_huge_zero_page(struct page *page) > > +bool is_huge_zero_page(struct page *page) > > { > > return ACCESS_ONCE(huge_zero_page) == page; > > } > > > > -static inline bool is_huge_zero_pmd(pmd_t pmd) > > +bool is_huge_zero_pmd(pmd_t pmd) > > { > > return is_huge_zero_page(pmd_page(pmd)); > > } > > ^^^ And all these exports. A new function is_huge_zero_pfn() is added to mm/huge_memory.c and exported. Thanks. --GID0FwUMdk1T2AWN Content-Type: text/x-diff; charset=us-ascii Content-Disposition: attachment; filename="0001-smaps-should-deal-with-huge-zero-page-exactly-same-a.patch" --GID0FwUMdk1T2AWN--