From: Oleg Nesterov <oleg@redhat.com>
To: Song Liu <songliubraving@fb.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
akpm@linux-foundation.org, matthew.wilcox@oracle.com,
kirill.shutemov@linux.intel.com, kernel-team@fb.com,
william.kucharski@oracle.com, srikar@linux.vnet.ibm.com
Subject: Re: [PATCH v3 1/2] khugepaged: enable collapse pmd for pte-mapped THP
Date: Fri, 2 Aug 2019 18:21:36 +0200 [thread overview]
Message-ID: <20190802162136.GA2539@redhat.com> (raw)
In-Reply-To: <20190801184823.3184410-2-songliubraving@fb.com>
On 08/01, Song Liu wrote:
>
> +static int khugepaged_add_pte_mapped_thp(struct mm_struct *mm,
> + unsigned long addr)
> +{
> + struct mm_slot *mm_slot;
> + int ret = 0;
> +
> + /* hold mmap_sem for khugepaged_test_exit() */
> + VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm);
> + VM_BUG_ON(addr & ~HPAGE_PMD_MASK);
> +
> + if (unlikely(khugepaged_test_exit(mm)))
> + return 0;
> +
> + if (!test_bit(MMF_VM_HUGEPAGE, &mm->flags) &&
> + !test_bit(MMF_DISABLE_THP, &mm->flags)) {
> + ret = __khugepaged_enter(mm);
> + if (ret)
> + return ret;
> + }
see my reply to v2
> +void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long haddr)
> +{
> + struct vm_area_struct *vma = find_vma(mm, haddr);
> + pmd_t *pmd = mm_find_pmd(mm, haddr);
> + struct page *hpage = NULL;
> + unsigned long addr;
> + spinlock_t *ptl;
> + int count = 0;
> + pmd_t _pmd;
> + int i;
> +
> + VM_BUG_ON(haddr & ~HPAGE_PMD_MASK);
> +
> + if (!vma || !vma->vm_file || !pmd)
^^^^^^^^^^^^^
I am not sure this is enough,
> + return;
> +
> + /* step 1: check all mapped PTEs are to the right huge page */
> + for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
> + pte_t *pte = pte_offset_map(pmd, addr);
> + struct page *page;
> +
> + if (pte_none(*pte))
> + continue;
> +
> + page = vm_normal_page(vma, addr, *pte);
Why can't vm_normal_page() return NULL? Again, we do not if this vm_file
is the same shmem_file() or something else.
And in fact I don't think it is safe to use vm_normal_page(vma, addr)
unless you know that vma includes this addr.
to be honest, I am not even sure that unconditional mm_find_pmd() is safe
if this "something else" is really special.
Oleg.
next prev parent reply other threads:[~2019-08-02 16:21 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-01 18:48 [PATCH v3 0/2] khugepaged: collapse pmd for pte-mapped THP Song Liu
2019-08-01 18:48 ` [PATCH v3 1/2] khugepaged: enable " Song Liu
2019-08-02 16:21 ` Oleg Nesterov [this message]
2019-08-02 20:34 ` Song Liu
2019-08-01 18:48 ` [PATCH v3 2/2] uprobe: collapse THP pmd after removing all uprobes Song Liu
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