Messages in this thread Patch in this message | | | Date | Wed, 26 Oct 2005 12:48:31 +1000 | From | David Gibson <> | Subject | Re: RFC: Cleanup / small fixes to hugetlb fault handling |
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On Wed, Oct 26, 2005 at 12:00:55PM +1000, David Gibson wrote: > Hi, Adam, Bill, Hugh, > > Does this look like a reasonable patch to send to akpm for -mm.
Ahem. Or rather this version, which actually compiles.
This patch makes some slight tweaks / cleanups to the fault handling path for huge pages in -mm. My main motivation is to make it simpler to fit COW in, but along the way it addresses a few minor problems with the existing code:
- The check against i_size was duplicated: once in find_lock_huge_page() and again in hugetlb_fault() after taking the page_table_lock. We only really need the locked one, so remove the other.
- find_lock_huge_page() didn't, in fact, lock the page if it newly allocated one, rather than finding it in the page cache already. As far as I can tell this is a bug, so the patch corrects it.
- find_lock_huge_page() isn't a great name, since it does extra things not analagous to find_lock_page(). Rename it find_or_alloc_huge_page() which is closer to the mark.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Index: working-2.6/mm/hugetlb.c =================================================================== --- working-2.6.orig/mm/hugetlb.c 2005-10-26 11:18:39.000000000 +1000 +++ working-2.6/mm/hugetlb.c 2005-10-26 12:46:29.000000000 +1000 @@ -336,32 +336,28 @@ flush_tlb_range(vma, start, end); } -static struct page *find_lock_huge_page(struct address_space *mapping, - unsigned long idx) +static struct page *find_or_alloc_huge_page(struct address_space *mapping, + unsigned long idx) { struct page *page; int err; - struct inode *inode = mapping->host; - unsigned long size; retry: page = find_lock_page(mapping, idx); if (page) - goto out; - - /* Check to make sure the mapping hasn't been truncated */ - size = i_size_read(inode) >> HPAGE_SHIFT; - if (idx >= size) - goto out; + return page; if (hugetlb_get_quota(mapping)) - goto out; + return NULL; + page = alloc_huge_page(); if (!page) { hugetlb_put_quota(mapping); - goto out; + return NULL; } + lock_page(page); + err = add_to_page_cache(page, mapping, idx, GFP_KERNEL); if (err) { put_page(page); @@ -370,50 +366,49 @@ goto retry; page = NULL; } -out: + return page; } -int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, - unsigned long address, int write_access) +int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma, + unsigned long address, pte_t *ptep) { - int ret = VM_FAULT_SIGBUS; + int ret; unsigned long idx; unsigned long size; - pte_t *pte; struct page *page; struct address_space *mapping; - pte = huge_pte_alloc(mm, address); - if (!pte) - goto out; - mapping = vma->vm_file->f_mapping; idx = ((address - vma->vm_start) >> HPAGE_SHIFT) + (vma->vm_pgoff >> (HPAGE_SHIFT - PAGE_SHIFT)); - /* - * Use page lock to guard against racing truncation - * before we get page_table_lock. - */ - page = find_lock_huge_page(mapping, idx); + /* This returns a locked page, which keeps us safe in the + * event of a race with truncate() */ + page = find_or_alloc_huge_page(mapping, idx); if (!page) - goto out; + return VM_FAULT_SIGBUS; spin_lock(&mm->page_table_lock); + + ret = VM_FAULT_SIGBUS; + size = i_size_read(mapping->host) >> HPAGE_SHIFT; if (idx >= size) goto backout; ret = VM_FAULT_MINOR; - if (!pte_none(*pte)) + + if (!pte_none(*ptep)) + /* oops, someone instantiated this PTE before us */ goto backout; add_mm_counter(mm, file_rss, HPAGE_SIZE / PAGE_SIZE); - set_huge_pte_at(mm, address, pte, make_huge_pte(vma, page)); + set_huge_pte_at(mm, address, ptep, make_huge_pte(vma, page)); + spin_unlock(&mm->page_table_lock); unlock_page(page); -out: + return ret; backout: @@ -421,7 +416,30 @@ hugetlb_put_quota(mapping); unlock_page(page); put_page(page); - goto out; + + return ret; +} + +int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, + unsigned long address, int write_access) +{ + pte_t *ptep; + pte_t entry; + + ptep = huge_pte_alloc(mm, address); + if (! ptep) + /* OOM */ + return VM_FAULT_SIGBUS; + + entry = *ptep; + + if (pte_none(entry)) + return hugetlb_no_page(mm, vma, address, ptep); + + /* we could get here if another thread instantiated the pte + * before the test above */ + + return VM_FAULT_SIGBUS; } int follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
-- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/people/dgibson - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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