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Date: Wed, 24 Mar 2010 14:57:25 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc: LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Andi Kleen <andi@...stfloor.org>,
Wu Fengguang <fengguang.wu@...el.com>,
Matt Mackall <mpm@...enic.com>,
Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Subject: Re: [PATCH -mmotm] [BUGFIX] pagemap: fix pfn calculation for
hugepage
On Wed, 24 Mar 2010 14:42:27 +0900
Naoya Horiguchi <n-horiguchi@...jp.nec.com> wrote:
> When we look into pagemap using page-types with option -p, the value
> of pfn for hugepages looks wrong (see below.)
> This is because pte was evaluated only once for one vma
> although it should be updated for each hugepage. This patch fixes it.
>
> $ page-types -p 3277 -Nl -b huge
> voffset offset len flags
> 7f21e8a00 11e400 1 ___U___________H_G________________
> 7f21e8a01 11e401 1ff ________________TG________________
> ^^^
> 7f21e8c00 11e400 1 ___U___________H_G________________
> 7f21e8c01 11e401 1ff ________________TG________________
> ^^^
>
> One hugepage contains 1 head page and 511 tail pages in x86_64 and
> each two lines represent each hugepage. Voffset and offset mean
> virtual address and physical address in the page unit, respectively.
> The different hugepages should not have the same offset value.
>
> With this patch applied:
>
> $ page-types -p 3386 -Nl -b huge
> voffset offset len flags
> 7fec7a600 112c00 1 ___UD__________H_G________________
> 7fec7a601 112c01 1ff ________________TG________________
> ^^^
> 7fec7a800 113200 1 ___UD__________H_G________________
> 7fec7a801 113201 1ff ________________TG________________
> ^^^
> OK
>
> Changelog:
> - add hugetlb entry walker in mm/pagewalk.c
> (the idea based on Kamezawa-san's patch)
>
Seems good.
More info.
- This patch modifies walk_page_range()'s hugepage walker.
But the change only affects pagemap_read(), it's only caller of hugepage callback.
- Before patch, hugetlb_entry() callback is called once per pgd. Then,
hugtlb_entry() has to walk pgd's contents by itself.
This caused BUG.
- After patch, hugetlb_entry() callback is called once per hugepte entry.
Then, callback will be much simpler.
> Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
> fs/proc/task_mmu.c | 27 +++++++--------------------
> include/linux/mm.h | 4 ++--
> mm/pagewalk.c | 47 +++++++++++++++++++++++++++++++++++++----------
> 3 files changed, 46 insertions(+), 32 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 2a3ef17..9635f0b 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -662,31 +662,18 @@ static u64 huge_pte_to_pagemap_entry(pte_t pte, int offset)
> return pme;
> }
>
> -static int pagemap_hugetlb_range(pte_t *pte, unsigned long addr,
> - unsigned long end, struct mm_walk *walk)
> +/* This function walks within one hugetlb entry in the single call */
> +static int pagemap_hugetlb_range(pte_t *pte, unsigned long hmask,
> + unsigned long addr, unsigned long end,
> + struct mm_walk *walk)
> {
> - struct vm_area_struct *vma;
> struct pagemapread *pm = walk->private;
> - struct hstate *hs = NULL;
> int err = 0;
> + u64 pfn;
>
> - vma = find_vma(walk->mm, addr);
> - if (vma)
> - hs = hstate_vma(vma);
> for (; addr != end; addr += PAGE_SIZE) {
> - u64 pfn = PM_NOT_PRESENT;
> -
> - if (vma && (addr >= vma->vm_end)) {
> - vma = find_vma(walk->mm, addr);
> - if (vma)
> - hs = hstate_vma(vma);
> - }
> -
> - if (vma && (vma->vm_start <= addr) && is_vm_hugetlb_page(vma)) {
> - /* calculate pfn of the "raw" page in the hugepage. */
> - int offset = (addr & ~huge_page_mask(hs)) >> PAGE_SHIFT;
> - pfn = huge_pte_to_pagemap_entry(*pte, offset);
> - }
> + int offset = (addr & ~hmask) >> PAGE_SHIFT;
> + pfn = huge_pte_to_pagemap_entry(*pte, offset);
> err = add_to_pagemap(addr, pfn, pm);
> if (err)
> return err;
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 3899395..24f198e 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -783,8 +783,8 @@ struct mm_walk {
> int (*pmd_entry)(pmd_t *, unsigned long, unsigned long, struct mm_walk *);
> int (*pte_entry)(pte_t *, unsigned long, unsigned long, struct mm_walk *);
> int (*pte_hole)(unsigned long, unsigned long, struct mm_walk *);
> - int (*hugetlb_entry)(pte_t *, unsigned long, unsigned long,
> - struct mm_walk *);
> + int (*hugetlb_entry)(pte_t *, unsigned long,
> + unsigned long, unsigned long, struct mm_walk *);
> struct mm_struct *mm;
> void *private;
> };
> diff --git a/mm/pagewalk.c b/mm/pagewalk.c
> index 7b47a57..f77a568 100644
> --- a/mm/pagewalk.c
> +++ b/mm/pagewalk.c
> @@ -80,6 +80,37 @@ static int walk_pud_range(pgd_t *pgd, unsigned long addr, unsigned long end,
> return err;
> }
>
> +#ifdef CONFIG_HUGETLB_PAGE
> +static unsigned long hugetlb_entry_end(struct hstate *h, unsigned long addr,
> + unsigned long end)
> +{
> + unsigned long boundary = (addr & huge_page_mask(h)) + huge_page_size(h);
> + return boundary < end ? boundary : end;
> +}
> +
> +static int walk_hugetlb_range(struct vm_area_struct *vma,
> + unsigned long addr, unsigned long end,
> + struct mm_walk *walk)
> +{
> + struct hstate *h = hstate_vma(vma);
> + unsigned long next;
> + unsigned long hmask = huge_page_mask(h);
> + pte_t *pte;
> + int err = 0;
> +
> + do {
> + next = hugetlb_entry_end(h, addr, end);
> + pte = huge_pte_offset(walk->mm, addr & hmask);
> + if (pte && walk->hugetlb_entry)
> + err = walk->hugetlb_entry(pte, hmask, addr, next, walk);
> + if (err)
> + return err;
> + } while (addr = next, addr != end);
> +
> + return err;
> +}
nitpick.
seems nicer than mine but "return 0" is ok if you add "return err" in the loop.
Thanks,
-Kame
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