Re: [PATCH 1/9] add defrag flags

Joel Schopp
2005-09-27T18:38:26Z

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> Looks like he made the same mistake in the actual code comments:
>
> +/* Allocation type modifiers, group together if possible
> + * __GPF_USER: Allocation for user page or a buffer page
> + * __GFP_KERNRCLM: Short-lived or reclaimable kernel allocation
> + */
> +#define __GFP_USER 0x40000u /* Kernel page that is easily reclaimable */
> +#define __GFP_KERNRCLM 0x80000u /* User is a userspace user */
>
> I'd guess you meant to write more like the following:
>
> #define __GFP_USER 0x40000u /* Page for user address space */
> #define __GFP_KERNRCLM 0x80000u /* Kernel page that is easily reclaimable */

Yep.

>
> And the block comment seems to needlessly repeat the inline comments,
> add a dubious claim, and omit the interesting stuff ... In other words:
>
> Does it actually matter if these two bits are grouped, or not? I
> suspect that some of your other code, such as shifting the gfpmask by
> RCLM_SHIFT bits, _requires_ that these two bits be adjacent. So the
> "if possible" in the comment above is misleading.
>
> And I suspect that gfp.h should contain the RCLM_SHIFT define, or
> at least mention in comment that RCLM_SHIFT depends on the position
> of the above two __GFP_* bits.

I'll add a comment here.

>
> And I don't see any mention in the comments in gfp.h that these
> two bits, in tandem, have an additional meaning - both bits off
> means, I guess, not reclaimable, well at least not easily.

Yep, adding comment now.

>
> My HARDWALL patch appears to already be in Linus's kernel, so you
> probably also need to do a global substitute of all instances in
> the kernel of __GFP_HARDWALL, replacing it with __GFP_USER. Here
> is the list of files I see affected, with a count of the number of
> __GFP_HARDWALL strings in each:
>
> include/linux/gfp.h:4
> kernel/cpuset.c:6
> mm/page_alloc.c:2
> mm/vmscan.c:4

We may not be able to use the same flag after all due to our need to mark buffer
pages as user.

>
> The comment in the next line looks like it needs to be changed to match
> the code change:
>
> +#define __GFP_BITS_SHIFT 21 /* Room for 20 __GFP_FOO bits */

Yep.

>
> On the other hand, why did you change __GFP_BITS_SHIFT? Isn't 20
> enough - just enough?

Yep.

Fixed patch attached.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Joel Schopp <jschopp@austin.ibm.com>

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Index: 2.6.13-joel2/fs/buffer.c
===================================================================
--- 2.6.13-joel2.orig/fs/buffer.c 2005-09-13 14:54:13.%N -0500
+++ 2.6.13-joel2/fs/buffer.c 2005-09-13 15:02:01.%N -0500
@@ -1119,7 +1119,8 @@ grow_dev_page(struct block_device *bdev,
struct page *page;
struct buffer_head *bh;

- page = find_or_create_page(inode->i_mapping, index, GFP_NOFS);
+ page = find_or_create_page(inode->i_mapping, index,
+ GFP_NOFS | __GFP_USER);
if (!page)
return NULL;

@@ -3044,7 +3045,8 @@ static void recalc_bh_state(void)

struct buffer_head *alloc_buffer_head(unsigned int __nocast gfp_flags)
{
- struct buffer_head *ret = kmem_cache_alloc(bh_cachep, gfp_flags);
+ struct buffer_head *ret = kmem_cache_alloc(bh_cachep,
+ gfp_flags|__GFP_KERNRCLM);
if (ret) {
preempt_disable();
__get_cpu_var(bh_accounting).nr++;
Index: 2.6.13-joel2/fs/dcache.c
===================================================================
--- 2.6.13-joel2.orig/fs/dcache.c 2005-09-13 14:54:14.%N -0500
+++ 2.6.13-joel2/fs/dcache.c 2005-09-13 15:02:01.%N -0500
@@ -721,7 +721,7 @@ struct dentry *d_alloc(struct dentry * p
struct dentry *dentry;
char *dname;

- dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL);
+ dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL|__GFP_KERNRCLM);
if (!dentry)
return NULL;

Index: 2.6.13-joel2/fs/ext2/super.c
===================================================================
--- 2.6.13-joel2.orig/fs/ext2/super.c 2005-09-13 14:54:14.%N -0500
+++ 2.6.13-joel2/fs/ext2/super.c 2005-09-13 15:02:01.%N -0500
@@ -138,7 +138,8 @@ static kmem_cache_t * ext2_inode_cachep;
static struct inode *ext2_alloc_inode(struct super_block *sb)
{
struct ext2_inode_info *ei;
- ei = (struct ext2_inode_info *)kmem_cache_alloc(ext2_inode_cachep, SLAB_KERNEL);
+ ei = (struct ext2_inode_info *)kmem_cache_alloc(ext2_inode_cachep,
+ SLAB_KERNEL|__GFP_KERNRCLM);
if (!ei)
return NULL;
#ifdef CONFIG_EXT2_FS_POSIX_ACL
Index: 2.6.13-joel2/fs/ext3/super.c
===================================================================
--- 2.6.13-joel2.orig/fs/ext3/super.c 2005-09-13 14:54:14.%N -0500
+++ 2.6.13-joel2/fs/ext3/super.c 2005-09-13 15:02:01.%N -0500
@@ -440,7 +440,7 @@ static struct inode *ext3_alloc_inode(st
{
struct ext3_inode_info *ei;

- ei = kmem_cache_alloc(ext3_inode_cachep, SLAB_NOFS);
+ ei = kmem_cache_alloc(ext3_inode_cachep, SLAB_NOFS|__GFP_KERNRCLM);
if (!ei)
return NULL;
#ifdef CONFIG_EXT3_FS_POSIX_ACL
Index: 2.6.13-joel2/fs/ntfs/inode.c
===================================================================
--- 2.6.13-joel2.orig/fs/ntfs/inode.c 2005-09-13 14:54:14.%N -0500
+++ 2.6.13-joel2/fs/ntfs/inode.c 2005-09-13 15:05:53.%N -0500
@@ -317,7 +317,7 @@ struct inode *ntfs_alloc_big_inode(struc
ntfs_inode *ni;

ntfs_debug("Entering.");
- ni = kmem_cache_alloc(ntfs_big_inode_cache, SLAB_NOFS);
+ ni = kmem_cache_alloc(ntfs_big_inode_cache, SLAB_NOFS|__GFP_KERNRCLM);
if (likely(ni != NULL)) {
ni->state = 0;
return VFS_I(ni);
@@ -342,7 +342,7 @@ static inline ntfs_inode *ntfs_alloc_ext
ntfs_inode *ni;

ntfs_debug("Entering.");
- ni = kmem_cache_alloc(ntfs_inode_cache, SLAB_NOFS);
+ ni = kmem_cache_alloc(ntfs_inode_cache, SLAB_NOFS|__GFP_KERNRCLM);
if (likely(ni != NULL)) {
ni->state = 0;
return ni;
Index: 2.6.13-joel2/include/linux/gfp.h
===================================================================
--- 2.6.13-joel2.orig/include/linux/gfp.h 2005-09-13 14:54:17.%N -0500
+++ 2.6.13-joel2/include/linux/gfp.h 2005-09-27 12:53:13.%N -0500
@@ -41,6 +41,16 @@ struct vm_area_struct;
#define __GFP_NOMEMALLOC 0x10000u /* Don't use emergency reserves */
#define __GFP_NORECLAIM 0x20000u /* No realy zone reclaim during allocation */

+/* Allocation type modifiers, these are required to be adjacent
+ * __GPF_USER: Allocation for user page or a buffer page
+ * __GFP_KERNRCLM: Short-lived or reclaimable kernel allocation
+ * Both bits off: Kernel non-reclaimable or very hard to reclaim
+ * RCLM_SHIFT (defined elsewhere) depends on the location of these bits
+ */
+#define __GFP_USER 0x40000u /* User is a userspace user */
+#define __GFP_KERNRCLM 0x80000u /* Kernel page that is easily reclaimable */
+#define __GFP_RCLM_BITS (__GFP_USER|__GFP_KERNRCLM)
+
#define __GFP_BITS_SHIFT 20 /* Room for 20 __GFP_FOO bits */
#define __GFP_BITS_MASK ((1 << __GFP_BITS_SHIFT) - 1)

@@ -48,14 +58,15 @@ struct vm_area_struct;
#define GFP_LEVEL_MASK (__GFP_WAIT|__GFP_HIGH|__GFP_IO|__GFP_FS| \
__GFP_COLD|__GFP_NOWARN|__GFP_REPEAT| \
__GFP_NOFAIL|__GFP_NORETRY|__GFP_NO_GROW|__GFP_COMP| \
- __GFP_NOMEMALLOC|__GFP_NORECLAIM)
+ __GFP_NOMEMALLOC|__GFP_KERNRCLM|__GFP_USER)

#define GFP_ATOMIC (__GFP_HIGH)
#define GFP_NOIO (__GFP_WAIT)
#define GFP_NOFS (__GFP_WAIT | __GFP_IO)
#define GFP_KERNEL (__GFP_WAIT | __GFP_IO | __GFP_FS)
-#define GFP_USER (__GFP_WAIT | __GFP_IO | __GFP_FS)
-#define GFP_HIGHUSER (__GFP_WAIT | __GFP_IO | __GFP_FS | __GFP_HIGHMEM)
+#define GFP_USER (__GFP_WAIT | __GFP_IO | __GFP_FS | __GFP_USER)
+#define GFP_HIGHUSER (__GFP_WAIT | __GFP_IO | __GFP_FS | __GFP_HIGHMEM | \
+ __GFP_USER)

/* Flag - indicates that the buffer will be suitable for DMA. Ignored on some
platforms, used as appropriate on others */