Re: [RFC/PATCH] prepare_unmapped_area

[Adam Litke <agl@us.ibm.com>]

On Tue, 2007-02-06 at 16:04 +1100, Benjamin Herrenschmidt wrote:
> Hi folks !
> 
> On Cell, I have, for performance reasons, a need to create special
> mappings of SPEs that use a different page size as the system base page
> size _and_ as the huge page size.
> 
> Due to the way the PowerPC memory management works, however, I can only
> have one page size per "segment" of 256MB (or 1T) and thus after such a
> mapping have been created in its own segment, I need to constraint
> -other- vma's to stay out of that area.
> 
> This currently cannot be done with the existing arch hooks (because of
> MAP_FIXED). However, the hugetlbfs code already has a hack in there to
> do the exact same thing for huge pages. Thus, this patch moves that hack
> into something that can be overriden by the architectures. This approach
> was choosen as the less ugly of the uglies after discussing with Nick
> Piggin. If somebody has a better idea, I'd love to hear it.

Hi Ben.  Would my patch from last Jan 31 entitled "[PATCH 5/6] Abstract
is_hugepage_only_range" (attached for your convienence) solve this
problem?

commit ef36c6c859d37ac40f0bd12d08f41f103ab76657
Author: litke@us.ibm.com <aglitke@kernel.localdomain>
Date:   Tue Jan 16 08:57:16 2007 -0800

    Abstract is_hugepage_only_range
    
    Some architectures define regions of the address space that can be used
    exclusively for either normal pages or hugetlb pages.  Currently,
    prepare_hugepage_range() is used to validate an unmapped_area for use with
    hugepages and is_hugepage_only_range() is used to validate an unmapped_area for
    normal pages.
    
    Introduce a prepare_unmapped_area() file operation to abstract the validation
    of unmapped areas.  If prepare_unmapped_area() is not specified, the default
    behavior is to require the area to not overlap any "special" areas.
    
    Buh-bye to another is_file_hugepages() call.
    
    Signed-off-by: Adam Litke <agl@us.ibm.com>

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index b61592f..3eea7a5 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -561,6 +561,7 @@ const struct file_operations hugetlbfs_file_operations = {
 	.mmap			= hugetlbfs_file_mmap,
 	.fsync			= simple_sync_file,
 	.get_unmapped_area	= hugetlb_get_unmapped_area,
+	.prepare_unmapped_area	= prepare_hugepage_range,
 };
 
 static struct inode_operations hugetlbfs_dir_inode_operations = {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 1410e53..853a4f4 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1094,6 +1094,7 @@ struct file_operations {
 	ssize_t (*sendfile) (struct file *, loff_t *, size_t, read_actor_t, void *);
 	ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
 	unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
+	int (*prepare_unmapped_area)(unsigned long addr, unsigned long len, pgoff_t pgoff);
 	int (*check_flags)(int);
 	int (*dir_notify)(struct file *filp, unsigned long arg);
 	int (*flock) (struct file *, int, struct file_lock *);
diff --git a/mm/mmap.c b/mm/mmap.c
index a5cb0a5..f8e0bd0 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1374,20 +1374,17 @@ get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
 		return -ENOMEM;
 	if (addr & ~PAGE_MASK)
 		return -EINVAL;
-	if (file && is_file_hugepages(file))  {
-		/*
-		 * Check if the given range is hugepage aligned, and
-		 * can be made suitable for hugepages.
-		 */
-		ret = prepare_hugepage_range(addr, len, pgoff);
-	} else {
-		/*
-		 * Ensure that a normal request is not falling in a
-		 * reserved hugepage range.  For some archs like IA-64,
-		 * there is a separate region for hugepages.
-		 */
+	/*
+	 * This file may only be able to be mapped into special areas of the
+	 * addess space (eg. hugetlb pages).  If prepare_unmapped_area() is
+	 * specified, use it to validate the selected range.  If not, just
+	 * make sure the range does not overlap any special ranges.
+	 */
+	if (file && file->f_op && file->f_op->prepare_unmapped_area)
+		ret = file->f_op->prepare_unmapped_area(addr, len, pgoff);
+	else
 		ret = is_hugepage_only_range(current->mm, addr, len);
-	}
+
 	if (ret)
 		return -EINVAL;
 	return addr;

-- 
Adam Litke - (agl at us.ibm.com)
IBM Linux Technology Center

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