2014-08-19 오후 10:03, Jan Kara 쓴 글:
Hello,
On Tue 19-08-14 15:52:38, Gioh Kim wrote:
A buffer cache is allocated from movable area
because it is referred for a while and released soon.
But some filesystems are taking buffer cache for a long time
and it can disturb page migration.
A new API should be introduced to allocate buffer cache
with user specific flag.
For instance if user set flag to zero, buffer cache is allocated from
non-movable area.
Signed-off-by: Gioh Kim <gioh.kim@xxxxxxx>
---
fs/buffer.c | 52 +++++++++++++++++++++++++++++--------------
include/linux/buffer_head.h | 12 +++++++++-
2 files changed, 46 insertions(+), 18 deletions(-)
diff --git a/fs/buffer.c b/fs/buffer.c
index 8f05111..14f2f21 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -993,7 +993,7 @@ init_page_buffers(struct page *page, struct block_device *bdev,
*/
static int
grow_dev_page(struct block_device *bdev, sector_t block,
- pgoff_t index, int size, int sizebits)
+ pgoff_t index, int size, int sizebits, gfp_t gfp)
{
struct inode *inode = bdev->bd_inode;
struct page *page;
@@ -1002,10 +1002,10 @@ grow_dev_page(struct block_device *bdev, sector_t block,
int ret = 0; /* Will call free_more_memory() */
gfp_t gfp_mask;
- gfp_mask = mapping_gfp_mask(inode->i_mapping) & ~__GFP_FS;
- gfp_mask |= __GFP_MOVABLE;
+ gfp_mask = (mapping_gfp_mask(inode->i_mapping) & ~__GFP_FS) | gfp;
+
Hum, it seems a bit misleading that the 'gfp' flags are just or-ed to
mapping_gfp_mask(inode->i_mapping). Usually, passed gfp mask is just
directly used. There are also interfaces like pagecache_get_page() which
play more complex tricks with mapping_gfp_mask(). This would be yet another
convention which I don't think is desirable. I know Andrew suggested what
you wrote so I guess I have to settle this with him. Andrew?
I don't know mapping_gfp_mask(). I just add gfp at the original code.
Whould you tell me why it is undesirable?
/*
- * XXX: __getblk_slow() can not really deal with failure and
+ * XXX: __getblk_gfp() can not really deal with failure and
* will endlessly loop on improvised global reclaim. Prefer
* looping in the allocator rather than here, at least that
* code knows what it's doing.
@@ -1058,7 +1058,7 @@ failed:
* that page was dirty, the buffers are set dirty also.
*/
static int
-grow_buffers(struct block_device *bdev, sector_t block, int size)
+grow_buffers(struct block_device *bdev, sector_t block, int size, gfp_t gfp)
{
pgoff_t index;
int sizebits;
@@ -1085,11 +1085,12 @@ grow_buffers(struct block_device *bdev, sector_t block, int size)
}
/* Create a page with the proper size buffers.. */
- return grow_dev_page(bdev, block, index, size, sizebits);
+ return grow_dev_page(bdev, block, index, size, sizebits, gfp);
}
-static struct buffer_head *
-__getblk_slow(struct block_device *bdev, sector_t block, int size)
+struct buffer_head *
+__getblk_gfp(struct block_device *bdev, sector_t block,
+ unsigned size, gfp_t gfp)
{
/* Size must be multiple of hard sectorsize */
if (unlikely(size & (bdev_logical_block_size(bdev)-1) ||
@@ -1111,13 +1112,14 @@ __getblk_slow(struct block_device *bdev, sector_t block, int size)
if (bh)
return bh;
- ret = grow_buffers(bdev, block, size);
+ ret = grow_buffers(bdev, block, size, gfp);
if (ret < 0)
return NULL;
if (ret == 0)
free_more_memory();
}
}
+EXPORT_SYMBOL(__getblk_gfp);
/*
* The relationship between dirty buffers and dirty pages:
@@ -1381,12 +1383,7 @@ EXPORT_SYMBOL(__find_get_block);
struct buffer_head *
__getblk(struct block_device *bdev, sector_t block, unsigned size)
{
- struct buffer_head *bh = __find_get_block(bdev, block, size);
-
- might_sleep();
- if (bh == NULL)
- bh = __getblk_slow(bdev, block, size);
- return bh;
+ return __getblk_gfp(bdev, block, size, __GFP_MOVABLE);
}
EXPORT_SYMBOL(__getblk);
Why did you remove the __find_get_block() call? That looks like a bug.
@@ -1410,18 +1407,39 @@ EXPORT_SYMBOL(__breadahead);
* @size: size (in bytes) to read
*
* Reads a specified block, and returns buffer head that contains it.
+ * The page cache is allocated from movable area so that it can be migrated.
* It returns NULL if the block was unreadable.
*/
struct buffer_head *
__bread(struct block_device *bdev, sector_t block, unsigned size)
{
- struct buffer_head *bh = __getblk(bdev, block, size);
+ return __bread_gfp(bdev, block, size, __GFP_MOVABLE);
+}
+EXPORT_SYMBOL(__bread);
+
+/**
+ * __bread_gfp() - reads a specified block and returns the bh
+ * @bdev: the block_device to read from
+ * @block: number of block
+ * @size: size (in bytes) to read
+ * @gfp: page allocation flag
+ *
+ * Reads a specified block, and returns buffer head that contains it.
+ * The page cache can be allocated from non-movable area
+ * not to prevent page migration if you set gfp to zero.
+ * It returns NULL if the block was unreadable.
+ */
+struct buffer_head *
+__bread_gfp(struct block_device *bdev, sector_t block,
+ unsigned size, gfp_t gfp)
+{
+ struct buffer_head *bh = __getblk_gfp(bdev, block, size, gfp);
if (likely(bh) && !buffer_uptodate(bh))
bh = __bread_slow(bh);
return bh;
}
-EXPORT_SYMBOL(__bread);
+EXPORT_SYMBOL(__bread_gfp);
/*
* invalidate_bh_lrus() is called rarely - but not only at unmount.
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 324329c..a1d73fd 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -177,10 +177,14 @@ struct buffer_head *__find_get_block(struct block_device *bdev, sector_t block,
unsigned size);
struct buffer_head *__getblk(struct block_device *bdev, sector_t block,
unsigned size);
+struct buffer_head *__getblk_gfp(struct block_device *bdev, sector_t block,
+ unsigned size, gfp_t gfp);
void __brelse(struct buffer_head *);
void __bforget(struct buffer_head *);
void __breadahead(struct block_device *, sector_t block, unsigned int size);
struct buffer_head *__bread(struct block_device *, sector_t block, unsigned size);
+struct buffer_head *__bread_gfp(struct block_device *,
+ sector_t block, unsigned size, gfp_t gfp);
void invalidate_bh_lrus(void);
struct buffer_head *alloc_buffer_head(gfp_t gfp_flags);
void free_buffer_head(struct buffer_head * bh);
@@ -295,7 +299,13 @@ static inline void bforget(struct buffer_head *bh)
static inline struct buffer_head *
sb_bread(struct super_block *sb, sector_t block)
{
- return __bread(sb->s_bdev, block, sb->s_blocksize);
+ return __bread_gfp(sb->s_bdev, block, sb->s_blocksize, __GFP_MOVABLE);
+}
+
+static inline struct buffer_head *
+sb_bread_gfp(struct super_block *sb, sector_t block, gfp_t gfp)
+{
+ return __bread_gfp(sb->s_bdev, block, sb->s_blocksize, gfp);
}
I think Andrew was suggesting to provide sb_bread_unmovable() and
sb_getblk_unmovable() which would set appropriately. It is then more
obvious what are filesystems trying to do when using those functions...
I think the common interface is important.
If sb_getblk_unmovable() is obvious for the filesystem,
I will add some codes for getblk_unmovable() which calling __getblk_gfp(),
and sb_bread_unmovable() calling __bread_gfp().
If so, sb_bread_gfp is not necessary.
It might be like followings:
diff --git a/fs/buffer.c b/fs/buffer.c
index 14f2f21..35caf77 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1088,7 +1088,7 @@ grow_buffers(struct block_device *bdev, sector_t block, int siz
return grow_dev_page(bdev, block, index, size, sizebits, gfp);
}
-struct buffer_head *
+static struct buffer_head *
__getblk_gfp(struct block_device *bdev, sector_t block,
unsigned size, gfp_t gfp)
{
@@ -1119,7 +1119,13 @@ __getblk_gfp(struct block_device *bdev, sector_t block,
free_more_memory();
}
}
-EXPORT_SYMBOL(__getblk_gfp);
+
+struct buffer_head *getblk_unmovable(struct block_device *bdev, sector_t block,
+ unsigned size)
+{
+ return __getblk_gfp(bdev, block, size, 0);
+}
+EXPORT_SYMBOL(getblk_unmovable);
/*
* The relationship between dirty buffers and dirty pages:
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index a1d73fd..c5fb4fc 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -177,8 +177,8 @@ struct buffer_head *__find_get_block(struct block_device *bdev, s
unsigned size);
struct buffer_head *__getblk(struct block_device *bdev, sector_t block,
unsigned size);
-struct buffer_head *__getblk_gfp(struct block_device *bdev, sector_t block,
- unsigned size, gfp_t gfp);
+struct buffer_head *getblk_unmovable(struct block_device *bdev, sector_t block,
+ unsigned size);
void __brelse(struct buffer_head *);
void __bforget(struct buffer_head *);
void __breadahead(struct block_device *, sector_t block, unsigned int size);
@@ -303,9 +303,9 @@ sb_bread(struct super_block *sb, sector_t block)
}
static inline struct buffer_head *
-sb_bread_gfp(struct super_block *sb, sector_t block, gfp_t gfp)
+sb_bread_unmovable(struct super_block *sb, sector_t block)
{
- return __bread_gfp(sb->s_bdev, block, sb->s_blocksize, gfp);
+ return __bread_gfp(sb->s_bdev, block, sb->s_blocksize, 0);
}
static inline void
Is it better?
Thank you for your advice.
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