RE: FW: [PATCH 0/3] Demand faulting for huge pages

["Chen, Kenneth W" <kenneth.w.chen@intel.com>]

Rohit Seth wrote on Friday, October 07, 2005 2:29 PM
> On Fri, 2005-10-07 at 10:47 -0700, Adam Litke wrote:
> > If I were to spend time coding up a patch to remove truncation
> > support for hugetlbfs, would it be something other people would
> > want to see merged as well?
> 
> In its current form, there is very little use of huegtlb truncate
> functionality.  Currently it only allows reducing the size of hugetlb
> backing file.   
> 
> IMO it will be useful to keep and enhance this capability so that
> apps can dynamically reduce or increase the size of backing files
> (for example based on availability of memory at any time).

Yup, here is a patch to enhance that capability.  It is more of bring
ftruncate on hugetlbfs file a step closer to the same semantics for
file on other file systems.


---
Add expanding ftruncate to hugetlbfs.

Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>

--- linux-2.6.14-rc3/fs/hugetlbfs/inode.c.orig	2005-10-07 18:07:38.131373873 -0700
+++ linux-2.6.14-rc3/fs/hugetlbfs/inode.c	2005-10-08 00:31:15.951404405 -0700
@@ -327,20 +327,20 @@ hugetlb_vmtruncate_list(struct prio_tree
 	}
 }
 
-/*
- * Expanding truncates are not allowed.
- */
 static int hugetlb_vmtruncate(struct inode *inode, loff_t offset)
 {
 	unsigned long pgoff;
 	struct address_space *mapping = inode->i_mapping;
-
-	if (offset > inode->i_size)
-		return -EINVAL;
+	struct vm_area_struct *vma;
+	struct prio_tree_iter iter;
+	int ret = 0;
 
 	BUG_ON(offset & ~HPAGE_MASK);
 	pgoff = offset >> HPAGE_SHIFT;
 
+	if (offset > inode->i_size)
+		goto do_expand;
+
 	inode->i_size = offset;
 	spin_lock(&mapping->i_mmap_lock);
 	if (!prio_tree_empty(&mapping->i_mmap))
@@ -348,6 +348,18 @@ static int hugetlb_vmtruncate(struct ino
 	spin_unlock(&mapping->i_mmap_lock);
 	truncate_hugepages(mapping, offset);
 	return 0;
+
+do_expand:
+	spin_lock(&mapping->i_mmap_lock);
+	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, ULONG_MAX) {
+		ret = hugetlb_prefault(mapping, vma);
+		if (ret == 0)
+			inode->i_size = offset;
+		else
+			break;
+	}
+	spin_unlock(&mapping->i_mmap_lock);
+	return ret;
 }
 
 static int hugetlbfs_setattr(struct dentry *dentry, struct iattr *attr)
--- linux-2.6.14-rc3/mm/hugetlb.c.orig	2005-10-07 23:16:42.789349826 -0700
+++ linux-2.6.14-rc3/mm/hugetlb.c	2005-10-07 23:25:04.175085872 -0700
@@ -340,7 +340,7 @@ void zap_hugepage_range(struct vm_area_s
 
 int hugetlb_prefault(struct address_space *mapping, struct vm_area_struct *vma)
 {
-	struct mm_struct *mm = current->mm;
+	struct mm_struct *mm = vma->vm_mm;
 	unsigned long addr;
 	int ret = 0;
 
@@ -360,6 +360,8 @@ int hugetlb_prefault(struct address_spac
 			ret = -ENOMEM;
 			goto out;
 		}
+		if (pte_present(*pte))
+			continue;
 
 		idx = ((addr - vma->vm_start) >> HPAGE_SHIFT)
 			+ (vma->vm_pgoff >> (HPAGE_SHIFT - PAGE_SHIFT));

-
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